review for pdf - Imperial College London

The Blackett Laboratory

Department of Physics Review Faculty of Physical Sciences

2003

Preface from the Head of Department The Blackett Laboratory at Imperial College is the academic home for hundreds of physicists, from undergraduates to professors. When the building went up at the end of the 1950Õs it was said to be the most expensive departmental building in the country. ItÕs certainly one of the nicest to work in, but for some time has needed sprucing up. The department, with a lot of help from College put in very substantial resources to improve the infrastructure during 2003. Labs were refurbished, corridors moved and brightened up, and the entrance from Prince Consort Road given a whole new look. Visitors are now greeted by an attractive and well-lit social area, which seems always to be buzzing with activity. The department is flourishing, buoyed by our top ranking in the Research Assessment Exercise and by the high quality of our students who chose to study with us. Physics Department staff received many external awards and prizes during 2003. Professor Peter Dornan was elected to the Fellowship of the Royal Society for his work in high energy physics. Professor Joanna Haigh was awarded the Chree Medal and Prize of the Institute of Physics for her work in atmospheric physics. Professor Martin Plenio was awarded the Maxwell Prize of the Institute of Physics for his work on quantum information processing and quantum computing. Prof Donal Bradley was a member of the team awarded the Descartes Prize for work in molecular electronics and light emitting polymers. Prof Chris Dainty was awarded the Mees Medal and Prize of the Optical Society of America (and I was the OSAÕs President-Elect in 2003). EPSRC awarded a Senior Fellowship to Prof John Pendry FRS so that he could devote his time to research into the new metamaterials he has been pioneering. PPARC awarded Senior Fellowships to Prof Peter Cargill, Dr Ken Long, and Dr Michele Dougherty. Martin Plenio was awarded a Senior fellowship by the Royal Society and the Leverhulme Foundation. The student Physics Society had a really active year; they were recognized by the Institute of Physics through the award of its Òbest physics society award.Ó

Many new appointments were made to the academic staff in 2003. Following a major review of the Theoretical Physics Group, a new String Theory Initiative brought Profs Chris Hull and Jerome Gauntlett and Drs Fay Dowker and Dan Waldram to Imperial from Queen Mary. The new Centre for Cold Matter was formed led by Prof Ed Hinds and Dr Ben Sauer, who came to us from Sussex, and they already have a Bose-Einstein condensate running in their new labs. The High Energy Physics Group have launched a major new initiative in neutrino physics and we welcomed Prof David Wark and Dr Yoshi Uchida to the academic staff to lead this effort. Dr Ken Long in the HEP group organized a major conference at Imperial on the proposed new neutrino factory, and a highlight was a dinner in the Flight Gallery of the Science Museum with Lord Sainsbury, the Science Minister, as guest speaker. The department has played a lead role in the establishment of the new Mathematical Sciences Institute at Imperial, which will host major interdisciplinary research collaborations. The department has also done well in winning major Basic Technology grants from Research Councils UK in attosecond physics, plasma physics, optical imaging and condensed matter physics. The Photonics group led by Prof Paul French were awarded a major DTI Beacon Award for their work in biomedical imaging. All of these point to the continuing research vitality of the department. Finally let me end on a sad note: in 2003 we saw the deaths of two leading figures in the department: Prof Tony Stradling, who brought semiconductor physics to the department and guided our work in the department and within the IRC in Semiconductor Growth with huge distinction; and Dr Betty Johnson, who played a major role in the establishment of the Daphne Jackson Fellowship scheme for science returners as well as researching in condensed matter theory. P. L. Knight FRS Head of Department October 2004

The cover: A dramatic infrared image of a dust globule from NASA's SPITZER Space Telescope, with which the Astrophysics Group has a strong involvement.

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Condensed Matter Theory Head of Group: Professor D D Vvedensky Astrophysics

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Head of Group: Professor M Rowan-Robinson High Energy Physics

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Experimental Solid State Physics and Centre for Electronic Materials and Devices Head of Group: Professor D Bradley Page 10

Head of Group: Professor P J Dornan Optics Laser Consortium

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Head of Group: Professor P M W French

Director: Professor J P Marangos Page 19

Optics Quantum Optics and Laser Science

Plasma Physics

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Head of Group: Professor K M Krushelnick Page 25

Head of Group: Professor J P Marangos Page 28

Optics Photonics

Space and Atmospheric Physics Head of Group: Professor J E Harries

Theoretical Physics

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Head of Group: Professor K Stelle Page 34

For contact addresses see page 53 2

The Blackett Laboratory

http://www.imperial.ac.uk/physics

General Departmental Information Head of Department Professor P. L. Knight FRS Tel: 020 7594 7500 Fax: 020 7594 7504 e-mail: [email protected]

Associate Head of Department Professor R. W. Smith Tel: 020 7594 7501 Fax: 020 7594 7504 e-mail: [email protected]

Director of Resource Development Dr. R. G. Burns Tel: 020 7594 7700 Fax: 020 7594 7777 e-mail: [email protected]

Director of Undergraduate Studies Professor R. C. Thompson Tel: 020 7594 7505 Fax: 020 7594 7777 e-mail: [email protected]

Senior Tutor (Undergraduates) : Dr R. J. Forsyth Tel: 020 7594 7524 Fax: 020 7594 7777 e-mail: [email protected]

Director of Postgraduate Studies Dr J. Sedgbeer Tel: 020 794 7512 Fax: 020 794 7509 e-mail: [email protected]

Admissions Tutor (Undergraduates) : Professor W. G. Jones Tel: 020 7594 7513 Fax: 020 7594 7777 e-mail: [email protected]

Schools Liaison Officer Dr J. Hassard Tel: 020 7594 7792 Fax: 020 7823 8830 e-mail: [email protected]

Undergraduate and Postgraduate Studies Undergraduate Teaching (Queries about undergraduate admissions should be addressed to the Admissions Tutor)

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Schools Liaison

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http://www.imperial.ac.uk/options/

Postgraduate Studies -

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MSc Prospective postgraduate students interested in admission for an MSc course should contact the appropriate course organiser listed below. MSc in Optics and Photonics Dr. K. Weir, Tel: 020 7594 7723, Fax: 020 7594 7714, e-mail: [email protected] MSc in Quantum Fields and Fundamental Forces Dr. J. Halliwell, Tel: 020 7594 7831, Fax: 020 7594 7844, e-mail: [email protected]

PhD Those interested in admission for doctoral level research leading to the PhD degree should contact the Heads of Research Groups in subject areas of interest as listed opposite. The Director of Postgraduate Studies will be glad to advise on all general matters concerning the requirements for admission as a postgraduate student.

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Astrophysics

http://www.imperial.ac.uk/research/astro

Head of Group: Professor M. Rowan-Robinson

Building on the success of AMANDA-II, the largest neutrino telescope in the world, the international collaboration is currently constructing ICECUBE which when completed in 2008 will encompass 1 km3 of instrumented South Polar ice and should be sensitive enough to commence exploration of the neutrino observational window (Fig. 3).

Experimental Astrophysics T. J. Sumner, W. G. Jones (HEP), I. Liubarsky, J. J. Quenby, G. K. Rochester, H. Araujo, A. Bewick, C. Bungau (RAL), D. Davidge, J.V. Dawson, A. S. Howard (HEP), V. Lebedenko, C. G-Y. Lee (SPAT), R. Luscher, D. Shaul. Search for Dark Matter Particles Parts manufacture for ZEPLIN III, our next generation two-phase xenon detector for dark matter search, is now 95% complete. The dark matter search is looking for signatures of direct interactions of exotic new particles in the Boulby underground facility. Our work is being done within the UKDMC collaboration (RAL, Sheffield University, and Imperial) which currently has some of the best results in the world from a simpler single phase liquid xenon scintillation target, ZEPLIN I. This uses a pulse shape discrimination technique to separate the interesting nuclear recoil signals from the much more abundant background due to normal radioactivity in the instrument and its environment. ZEPLIN III (Fig.1) should achieve about 2 orders of magnitude better sensitivity within a few years and this will maintain our world leading position, and pave the

Figure 1: This shows one of the critical parts of ZEPLIN III, made out of pure copper with stainless steel feedthroughs, being vacuum tested. Very clean electronbeam welding has been used to weld both copper and stainless parts together.

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Figure 2: Inertial Sensor design work for LISA. A view of the engineering model of the Charge Manage-ment System for the European LISA Test Package (LTP) to be flown on LISA-PF, being developed under contract to ESA.

way for larger targets with up to 1 tonne of xenon. Gravitational Wave Astronomy The detailed design of the Charge Management System for the LISA Pathfinder technology precursor satellite to gravitational wave science mission, LISA, of the European Space Agency is complete (Fig. 2). We are developing an Engineering Model, both for ESA and NASA. This system is required by LISA to control the charge build-up on the isolated proof-masses, which form the mirrors for the large baseline interferometry between the three spacecraft in the constellation. Charge build-up is caused by cosmic-ray impacts on the spacecraft and proof-masses. Gravitational wave astronomy from space was highlighted as a high priority area for PPARC funding in the recent Government spending review, with additional earmarked central resource. PPARC have approved funding for Imperial to cover the LISA-PF European flight system. Neutrino Astrophysics: The Astrophysics Group is formally part of the AMANDA and ICECUBE collaborations. Our scientific interest is in the connection between neutrino emission and gravitational waves, which would be expected in some of the more extreme forms of collapse/explosion of astrophysical objects.

Figure 3: IceCube will occupy a volume of one cubic kilometre. Here we depict one of the 80 strings of optical modules (number and size not to scale). IceTop located at the surface, comprises an array of sensors to detect air showers. It will be used to calibrate IceCube and to conduct research on high-energy cosmic rays.

Galactic Astrophysics J. E. Drew, W. P. S. Meikle, Y. Unruh, L.Lucy, M. Pozzo, S. Sim, R. Kotak, J. Vink. Ha emission line survey of the Galaxy We are leading two large international collaborations that aim to explore the entire Milky Way for emission line stars and compact nebulae down to a limiting red magnitude of almost 20. By pushing down 500 times fainter than the 1960s-generation of Ha Galactic surveys, these programmes should increase the number of known emission line objects by more than a factor of 10 (Fig. 4). This in turn should revolutionise our understanding of the early and late stages

of stellar evolution Ð the latter, in particular, remain very poorly sketched out. In the southern hemisphere, we are engaged in spectroscopic follow-up of candidate emission line stars derived from the already complete Anglo-Australian Observatory Schmidt Ha Southern Galactic Plane Survey. We have already made one spectacular discovery of a rare and particularly extreme Wolf-Rayet (WO) star: this object increases the available Galactic sample to just 4 stars and also breaks the record for observed maximum wind speed (5750 km/s) and carbon abundance (C/He = 2.85, by mass). Young stars A continuing interest concerns the intimate circumstellar environments of young stars, at all masses, still accreting matter. The main observational tool used to explore these environments continues to be high (spectral) resolution spectropolarimetry, mostly performed on the often-observed, bright Ha emission line. In 2003, attention focused on the lower mass solar-type young stars (T Tauri stars). We wanted to learn if the T Tau stars exhibit the same polarimetric behaviour as the Herbig Ae stars Ð it is becoming evident they do, hinting at no real change in the accretion geometry between these two groups of stars. The best observations obtained were of RY Tau: these have demonstrated that the common presumption of no significant linear polarization changes across Ha in T Tau-star spectra is unfounded. The Sun as a star Work continues on modelling solar and stellar irradiance variations. We have produced very successful solar irradiance models, invoking only changes in the surface magnetic field, that fit the observed data on timescales from days to decades. For shorter timescales of days to hours, we have started to disentangle variability due to magnetic surface features and convection, and are investigating how this scales to stars with different spectral types. Our findings will aid detection of

Figure 4: A false-colour image derived from 2 overlapping exposures taken as part of the northern photometric Ha survey in the autumn of 2003. This is of a nebulous and dust-obscured field in Cygnus that contains no known objects. Red colour corresponds to stars and nebulosity emitting in Ha.

planetary transits made by the COROT mission. Numerical modelling of supernovae The previously-developed transition probabilities for Monte Carlo energy packets were used successfully to compute a NLTE solution for the outer layers of a type II supernova. Encouraged by this, work has started on applying the technique to the general time-dependent radiative transfer problem for supernovae ejecta. In parallel we have been developing object-oriented code, exploiting these same techniques, to achieve easy generalisation to 2- and 3-D media. Supernovae A major problem in understanding thermonuclear (Type Ia) supernovae is the nature of the progenitor - a particularly important problem since these supernovae have provided the key evidence for an accelerating universe. An important step would be the observation of circumstellar material. A 2003 highlight has been our discovery, using the United Kingdom Infrared Telescope, of a large mass of circumstellar dust around the peculiar Type Ia Supernova 2002ic. This followed the earlier discovery (by observers in Chile) of hydrogen in the supernova spectrum. Using the Very Large Telescope in Chile, we have also obtained conclusive evidence that the hydrogen must have been released as a wind by the progenitor.

Another major goal is to establish whether or not supernovae are major sources of interstellar dust. A major component of this work has been our recently completed infrared/ optical study of the Type IIn Supernova 1998S which has provided strong evidence of at least 10-3 solar masses of dust associated with this rather unusual type of supernova. While some of the dust actually formed in the progenitor wind, it is likely that the interaction of the supernova shock with the wind also created an ideal "nursery" where grains grew. Cosmology and Extragalactic Astrophysics M. Rowan-Robinson, S. Warren, A. Jaffe, K. Nandra, M. Fox, S. Dye, L. Mendes, R. Priddey, D. Clements, D. Rosa, T. Takagi, P.OÕNeill, D. Novikov, I. Valtchanov, K. dÕMellow, M. Vaccari Infrared and submillimeter surveys The first data have been received from the SWIRE Legacy Survey, being carried out with NASAÕs Space Infrared Telescope Facility (SPITZER), launched in August 2003. This is the largest survey project being carried out by SPITZER and is expected to yield over a million infrared galaxies, in the wavelength range 3 to 170mm (Fig. 5). The final band-merged catalogue from the ELAIS survey, carried out with ESAÕs Infrared Space Observatory, has now been released. The catalogue includes a high proportion of ultraluminous infrared galaxies. A new population of luminous cool galaxies has been identified, which may have implications for galaxy evolution theories. Photometric redshift techniques have proved powerful in probing the infrared galaxy population at reshifts 0.5-1.5. With collaborators at Kent, Sussex and Groningen, the Group has been working on the data analysis pipeline for the Japanese all sky far infrared survey mission, ASTRO-F, due for launch in August 2005. The Group continues to work on the SHADES 850 micron survey using the JCMT in Hawaii and on preparations for 5

ESAÕs Herschel submillimetre mission. Cosmic Backgrounds The Group continues its role in ongoing experiments measuring the anisotropy of the Cosmic Microwave Background (CMB) radiation. MAXIMA and BOOMERANG, the first experiments to use the CMB to unambiguously measure the geometry of the Universe, have turned their attention to the polarization of the CMB. Polarization can shore up these cosmological measurements and, eventually, probe the epoch of cosmic inflation that may have occurred in the first fractions of a second after the Big Bang. Meanwhile, Imperial is developing software for the analysis of data from the European Space AgencyÕs Planck Surveyor CMB satellite, due to be launched in 2007. The Group is also involved in the theoretical prediction of the background of Gravitational Radiation that, in EinsteinÕs General Relativity, should suffuse the Universe. We are calculating the radiation from the mergers of Black Holes, millions to billions times the mass of our sun, residing in the centres of galaxies. Eventually, these could be observed by the ESA satellite LISA (whose hardware is also being developed in the Group) and, in the more distant future, by NASAÕs Big Bang Observer satellite, in which Imperial Astrophysics has become involved and for which a concept study was just approved by NASA. X-rays We are nearing completion and installation at Imperial of the final version of the "Tartarus" database, which contains fully reduced data products for all ASCA observations of active galactic nuclei (AGN). Our large area, hard X-ray survey "SHEEP" has been completed, with followup Chandra observations and ground based optical spectroscopy now underway. We have performed detailed analysis of the X-ray time variability of several AGN, using RXTE and XMM-Newton data, in separate collaborations with Cambridge University, UCLA and the University of Crete. We have also used XMMNewton to constrain the iron-K line 6

Figure 5: An early image from NASAÕs SPITZER infrared telescope. It shows a composite of the famous galaxy Messier 81 as seen at infrared wavelengths. The blue colours corresponds to 3.6 micron emission from stars in the bulge of the galaxy, the yellow and red colours to dust emission at 5.8, 8 and 24 microns, from star forming clouds in the disk of the galaxy.

profile of the AGN IRAS 13349+2438, which shows evidence for the gravitational redshift of the black hole. Dark Matter mass profiles in galaxies A critical test of the cold dark matter (CDM) paradigm for structure formation is the measurement of the slope of the dark matter density profile in the central regions of galaxies. We have applied our new semi-linear inversion technique to the gravitational lens 0047-2808, to investigate this issue. The method uses all the flux information in an image, and consequently we obtain good constraints. The 95% confidence interval on the exponent of the inner power-law slope is consistent with the predictions of CDM simulations. We have reanalysed the available data on the kinematics of Lymanbreak galaxies (LBGs) at redshift z~3, comparing against the predictions of theories of galaxy formation. Our analysis resolves a controversy over the nature of LBGs favouring the low-mass starburst model, over the

alternative model of single galaxies at the centres of the most massive dark matter haloes at that epoch.

Condensed Matter Theory Head of Group: Professor D. D. Vvedensky Science of Complexity

Rainfall Viewed as Relaxational Events K. Christensen, O. B. Peters

K. Christensen Since the laws of physics are simple, how come nature isn't? When looking around, you find nature is apparently complex. The complexity manifests itself, for example, in emergent properties such as simple patterns, hierarchical structures, fractal structures or other scale-free behaviour. The overall objective of the science of complex systems is to address why nature is complex, not simple. Tangled Nature Model K. Christensen, S. A. Collobiano, H. J. Jensen The dynamics of the Tangled Nature model is defined on the micro evolutionary time scale via reproduction, with heredity, variation, and natural selection. Each organism reproduces with a rate that is linked to the individuals' genetic sequence and depends on the composition of the population in genotype space. Thus the micro evolutionary dynamics of the fitness landscape is regulated by, and regulates, the evolution of the species by means of the mutual interactions. At low mutation rate, the macro evolutionary pattern mimics the fossil data: periods of stasis, where the population is concentrated in a network of coexisting species, is interrupted by bursts of activity. As the mutation rate increases, the duration and the frequency of bursts increases. Eventually, when the mutation rate reaches a certain threshold, the population is spread evenly throughout the genotype space showing that natural selection only leads to multiple distinct species if adaptation is allowed time to cause fixation. The mutation threshold has been derived theoretically, thereby providing a valuable insight into how the microscopic dynamics of the model determine the observed macroscopic phenomena.

We demonstrate that self-organised criticality may offer an alternative to the chaos theoretic perspective on the subject of rainfall. From the point of view of energy flow through a non-equilibrium system, rainfall is analogous to other relaxational processes in Nature such as earthquakes. The Sun provides the energy to evaporate water from the oceans. This energy is stored in the atmosphere in form of vapour. Once in a while, the energy is released, causing a rainfall. The number density of rainfall events per year is inversely proportional to the released water column raised to the power 1.4. The event durations and the waiting times between events are also characterized by scaling regions, where no typical time scale exists. These findings are consistent with the concept of selforganised criticality, which refers to the tendency of slowly driven nonequilibrium systems to evolve into a state with scale free behaviour without the need to fine-tune any control parameters. Quantum Mechanical Modelling W. M. C. Foulkes Computer simulation is used in many different contexts, but the underlying questions are often surprisingly similar. What happens when many simple objects come together and interact? How does the complex behaviour of the whole emerge from the simple laws obeyed by its parts? The constituent objects range from the electrons and nuclei in a crystal of silicon to the cables and girders in a bridge, but the common aim is to predict the complex large scale behaviour from the simpler small scale behaviour. In almost all types of computer modelling, some of the data required for simulations on one length scale can only be obtained from the results of simulations on the length scale below. This descent to

http://www.imperial.ac.uk/research/cmth smaller and smaller length scales continues right down to the quantum mechanical scale (roughly 10-10 m) at which the many-electron Schršdinger equation at last provides a concise and accurate universal law of nature. There are quantum field theoretical levels below it, but the Schršdinger equation requires no input from these and serves as a natural root for the tree of simulations with branches at larger and larger length scales. Attempting a direct solution of the Schršdinger equation for a system of thousands of interacting electrons would have been considered an impossibility a decade ago, but we and a few other groups have shown that it can be done. The main errors in the quantum Monte Carlo (QMC) methods we use are statistical in nature and can be reduced simply by increasing the run time. Using large parallel computers, we can simulate systems containing several hundred atoms, which is enough to model most of the properties of most molecules and solids with great accuracy. During the past year we have continued our study of the electronic properties of surfaces, at which subtle electron-electron interaction effects are expected to be particularly important. These simulations have required several technical innovations, including a new method for dealing with Coulomb interactions in quasi-two-dimensional systems, but are now close to complete. We are also working on a new approach to the calculation of excitation spectra (more specifically, one and two-electron Green's functions) for real solids and molecules. If we succeed, we will have increased the usefulness and range of QMC methods substantially. Quantum Phases of Matter D. K. K. Lee, R. Jack When we put together a large collection of atoms or electrons, order may emerge from their complex cooperative behaviour. Examples include superconductivity and ferromagnetism. A central challenge in 7

condensed matter physics is the question: "how does the sum become more than its parts?" Theoretical progress in understanding such "emergent phenomena" can help us search for, and even design, new materials of practical importance. Tunnelling and Dissipation in Quantum Hall Ferromagnets D. K. K. Lee I have recently studied the "quantum Hall bilayer" which apparently violates the well-known Ohm's law for electrical conduction which states that the current should be proportional to the driving voltage. This system consists of two parallel two-dimensional electron gases in a strong magnetic field. These layers are in close proximity on the atomic scale in a GaAs heterostructure. The Coulomb interaction between the electrons in the two layers drives a quantum phase transition to an ordered state, akin to a ferromagnet (where all the magnetic moments point in the same direction). Experiments have shown that electrical transport across the two layers is drastically enhanced in these bilayers at low temperatures. Surprisingly, the current across the bilayer may increase when the voltage is decreased! This violation of Ohm's law occurs over a wide range of voltages at low temperature. We are the first to give a microscopic explanation of this phenomenon. We have shown that the loss of quantum coherence in this system is the key to this puzzle. The short-term goal of the project is to provide a theory of coherence in these systems which can be tested by experimentalists. Future research will explore how disorder play a role in decoherence. From a wider perspective, this system provides a testbed for ideas about decoherence in materials which exhibit quantum order (such as superconductors and ferromagnets). Understanding decoherence is crucial to fulfilling the promise of these systems as candidates for nanotechnological applications.

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Spintronics A. MacKinnon, E. A. Johnson 11/9/03, M. A. Oliveira The possibility of producing and manipulating a spin-polarised current has several exciting applications, most notably in quantum computing. Although the use of magnetic materials in such devices springs to mind there are also non-magnetic means of manipulating electron spins, particularly through the Rashba effect. Most work on this effect has started with the assumption that it is necessary to use an artificial anisotropic structure, such as a semiconductor quantum well sandwiched between two different wider gap semiconductors. Such systems have structural inversion asymmetry (SIA). Using a computer algorithm in which the properties of the layered semiconductor system are calculated atomic layer by atomic layer, we have been able to study the electronic properties of a range of realistic and artificial structures and gain a better understanding of the conditions necessary to separate electrons according to their spin state. A particularly significant result is that the SIA is not necessary. Most semiconductors, with the exception of Silicon and Germanium, have bulk inversion asymmetry (BIA). When a quantum well is formed by sandwiching these materials between wider gap semiconductors a spinsplitting can arise which may be an order of magnitude or more larger than that of the bulk material and comparable with that due to SIA. This result opens up new and unexpected possibilities for the design of spintronic structures. Disordered Systems with Interactions A. MacKinnon, J. M. Carter A full explanation of the physics of electrons in non-crystalline materials not only requires us to understand the role of disorder but also the interplay between disorder and electron-electron interactions. As disordered systems and interacting systems both represent difficult

problems in their own right, the combination presents particular challenges. At the present time it is only possible to make progress on simpler versions of the problem or using approximations whose validity is open to challenge. We have chosen to concentrate on 1-dimensional systems as a first step and have developed a computational algorithm combining elements of the traditional transfer matrix method for non-interacting disordered systems with the density matrix renormalisation group used for interacting systems. This approach has been applied to 3 models: a spinless chain, a spinless strip of width 2 and the 1D Hubbard model. In the 2 spinless models, unlike the corresponding non-interacting system there is a region of extended states when the interactions are attractive. Repulsive interactions by contrast tend to enhance the localisation effect. For the Hubbard model there is no extended regime and in general the effect is opposite to that of the spinless systems: repulsive interactions give rise to a screening effect which masks the disorder and reduces the localisation. The next step will be to generalise the approach to strips of finite cross section with a view to studying the behaviour of 2 and 3 dimensional systems using finite size scaling. Materials for Near Field Optics J. B. Pendry, S. A. Ramakrishna, S. R. L. Guenneau, V. Yannopapas, W. Williams Some time ago members of the Group showed that a slab of material with the unusual property of negative refractive index could act as a perfect lens whose resolution is unlimited by the wavelength. Gradually the realisation has dawned that something much more interesting is happening and that an alternate way of understanding properties of a negative slab is as a piece of negative space. Optically speaking, and only at the frequency for which the lens condition is satisfied, a slab of material with e® -1, m®-1 to annihilate the effect of an equal thickness of vacuum. Having realised this it is only one further step to prove a more general

to tunnel across the gap between the cylinders. A clue to the nature of these resonances is given by the closed loop of dotted rays in the centre of the figure which indicates the presence of a state which traps radiation i.e. we have a resonance. This elaboration of the perfect lens greatly increases the richness of the subject as a far greater variety of lens geometries can now be considered.

equations by invoking rigorous theorems from the theory of stochastic processes. The equivalence of the Langevin description and the lattice models is demonstrated by direct comparison with kinetic Monte Carlo simulations for several standard models of epitaxial growth, including the Edwards-Wilkinson and WolfVillain models for surface relaxation, and models with both deposition and surface diffusion. Theory of Quantum Dot Formation on Singular and Patterned Substrates

Figure 1. Above: an alternative pair of complementary media, each annihilating the effect of the other. Light does not necessarily follow a straight line path in each medium, but the overall effect is as if a section of space thickness 2d were removed from the experiment. Below: A graphical expression of our new theorem: complementary halves sum to zero. The optical properties of the rest of the system can be calculated by cutting out the media and closing the gap.

result: two slabs of material of equal thickness and placed adjacent to one another optically annihilate if one is the negative mirror image of the other, the mirror being taken to lie on the interface between the two slabs. A simple instance of this is shown schematically in Fig. 1. Although this result is quite plausible where rays follow a simple distorted trajectory in each medium as illustrated above, in some instances the theorem has startling consequences. Consider Fig. 2, a system drawn to my attention by David Smith of UCSD: the mirror theorem applies but a ray construction contradicts the theorem. Applying the laws of refraction to ray 2 implies that the ray is rejected by the system instead of being transmitted through to the other side and a dark shadow behind the cylinders is predicted by the ray picture. In fact a full solution of Maxwell's equations shows that ray 2 is transmitted and emerges through the system just like ray 1 and no shadow is formed. The apparent paradox is resolved by recognising that a series of resonances form on the surfaces of the cylinders and these resonances enable radiation

C. Haselwandter, D. D. Vvedensky

Figure 2. The left and right media in this 2D system are negative mirror images and therefore optically annihilate one another. However a ray construction appears to contradict this result. Nevertheless the theorem is correct and the ray construction erroneous. Note the closed loop of rays indicating the presence of resonances.

Equations of Motion for Driven Lattice Models A. Chua, C. Haselwandter, D. D. Vvedensky Many physical phenomena can be modelled as particles on a lattice that interact according to a set of prescribed rules. Such systems are called "lattice gases". The dynamics of lattice gases are generated by transition rates for site occupancies that are determined by the occupancies of neighboring sites at the preceding time step. This provides the basis for a multiscale approach to nonequilibrium systems in that atomistic processes are expressed as transition rates in a master equation, while a partial differential equation, derived from this master equation, embodies the macroscopic evolution of the coarsegrained system. Exact lattice Langevin equations for the height fluctuations in driven lattice growth models have been derived from their master

Semiconductor quantum dots offer the promise of many technological and scientific innovations, ranging from optoelectronics to quantum computing. All of these applications are based on the confinement of carriers within quantum dots to discrete energy levels, as well as a degree of spatial self-organization. The challenge for the practical implementation of quantum dot nanostructures requires understanding phenomena across a range of length and time scales. The nucleation process, though still not completely understood, requires a specific reconstruction and surface orientation. At a more coarsegrained level, continuum equations that describe the evolution of surface morphology abound, but none is yet capable of making detailed quantitative predictions on the influence of various factors on the ordering of quantum dots. We have derived a stochastic differential equations that captures the main effects of strain on the kinetics of quantum dot formation. It has been derived from a lattice model that reproduces many experimental features. This equation can be applied both to singular (flat) surfaces patterned substrates, where the patterning (with lithography) is used to create regular arrays of dots. The experimental validation of this model will be carried out in collaboration with the group of Eli Kapon at EPFL in Lausanne, Switzerland.

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Experimental Solid State Physics, http://www.imperial.ac.uk/research/exss Centre for Electronic Materials and Devices, and Centre for High Temperature Superconductivity Head of Group: Professor D.D.C. Bradley Our programme of research covers most aspects of modern experimental solid state physics including molecular electronic materials, soft condensed matter, quantum optics and photonics, magnetism, superconductivity and inorganic semiconductors. There is a strong emphasis on novel materials and structures and on applications in a wide range of devices. Selected examples of current interests include next generation thin film solar cells (using inorganic semiconductor quantum wells, nanostructured oxides and organic semiconductors), optical microcavities (weak and strong coupling structures and their photonic properties), quantum optics in solids (electromagnetically induced transparency and quantum light sources), ultrafast photonics for datacommunications (sources, amplifiers, optical routers and switches), quantum dots (as novel gain media and for extended wavelength range light emitting diodes (LEDs)), spectroscopic studies of soft matter (biomolecules, polymers), metrology for the life sciences (single molecule spectroscopy and microanalysis systems), spintronic devices, High Tc and MgB2 superconductors, SiSiGe electronics (solar cells and high speed transistors) and molecular electronic materials and devices (high efficiency LEDs for displays and lighting, TFTs for plastic electronics, and photodetectors). The group is strongly linked to the Centre for Electronic Materials and Devices (CEMD), which draws together people from the Departments of Physics, Chemistry, Electrical and Electronic Engineering and Materials into a wide range of interdisciplinary projects. Our activities are classified into three main sections, namely semiconductor optoelectronics, molecular electronic materials and applications, and transport and magnetism. 10

Semiconductor Optoelectronics K. W. J. Barnham, R. Murray, G. Parry, C. C. Philips, P. Stavrinou Quantum Dots E. Clarke, E. Le Ru, C. Roberts, R. Murray. (P. Howe, T. S. Jones (Chemistry) ) Self-assembled quantum dots (QDs) show strong 3-D carrier confinement and are frequently referred to as Ôartificial atomsÕ having discrete energy levels (see Fig. 1). They are grown by depositing InAs on GaAs, using molecular beam epitaxy where the lattice-mismatch-induced strain causes a 2D-3D transition into small InAs islands. Growth on GaAs, rather than the current standard InP, offers financial and technological advantages, particularly for structures that include distributed Bragg reflectors (resonant cavity LEDs and Vertical Cavity Surface Emitting lasers). After capping with GaAs these structures promise improved optical devices such as inplane lasers, optical amplifiers and triggered single photon sources for quantum cryptography. In addition, there is interest in coupled QDs as potential solid state ÔqubitsÕ for quantum computing applications.

One aim is to produce in-plane and vertical cavity lasers operating at telecommunications wavelengths around 1.3 Ð 1.55 microns. Devices operating at the shorter end of this range may be made using a very low InAs growth rate. Extending this to longer wavelengths is more difficult and the method we have developed (and patented) uses an underlying strain-reducing seed layer. Figure 1 shows that the E0 emission is now close to the upper limit of the required range. A second interest concerns Ôsingle photonÕ sources for secure quantum cryptography. It is impossible to generate single photons using weak pulses from laser beams since the photon number obeys Poisson statistics. The unique electronic structure of the QDs ensures that the last electronhole to recombine within the dot emits only one photon (confirmed via photon pair correlation experiments). However a single dot has to be excited and the emitted single photons detected (see Fig. 1). This again requires precision engineering of the dot properties (density, size, composition and strain-state) and the use of sophisticated near field optical spectroscopy techniques (micro PL).

(a) (b)

Figure 1(a): Emission spectrum of a seeded QD layer. The QD ground (s) state is denoted E0 and the excited states (p) E1 and (d) E2. The spectral width is due to variations in dot size and composition. The inset shows a scanning tunneling micrograph of a QD layer prior to capping. (b): Micro-PL spectra from a nominally 1 µm diameter mesa. Individual emission lines are resolved but they probably arise from a number of quantum dots. (Spectrum courtesy of Martin Ward, Toshiba Research Europe Ltd)

Novel Photovoltaic Structures K. W. J. Barnham, I. M. Ballard, A. Bessiere, A. J. Chatten, M. Mazzer, J. Zhang The worldÕs highest efficiency solar cells are monolithic tandem structures formed of GaInP and GaAs and their performance is limited by current generation in the lower band-gap GaAs cell. Our novel strain-balanced, quantum well solar cells (SB-QWSC) extend the absorption wavelength, allowing significant current enhancement while preserving good voltage performance. If our SB-QWSC were to replace the standard GaAs cell it would increase the tandem efficiency from 34% to 37% at Å 300 suns concentration. Tandem cells are already deployed on satellites but costs must be reduced using relatively cheap light concentrating systems before they can enter the terrestrial solar cell market. We plan to optimise our SB-QWSC within a tandem structure grown by MOVPE (EPSRC III-V Facility, Sheffield). The high efficiency could be exploited in novel, building integrated, concentrator systems being developed in an industrial collaboration. We have extended our fundamental work on the quasi-Fermi level separation in SB-QWSCs to the light-biased situation: This has important implications for ultimate cell efficiency. A novel, non-tracking concentrator, which uses the luminescence and quantum confinement properties of QD semiconductors is under development. We have established a thermodynamic model to maximise performance and have shown that the separation between luminescence and absorption can be optimised by varying the spread of quantum dot sizes. Finally, in collaboration with BP Solar we have studied epitaxially grown films of Si to investigate the ultimate efficiency achievable by thin film Si cells.

Sub-wavelength Technologies for Optoelectronic Components S. Klengel, P. Caillaud, C. Palmer, P. N. Stavrinou, J. Heffernan (SLE), G. Parry We have a strong interest in the use of sub-wavelength structures in optoelectronic environments. The structures currently under investigation involve Photonic Crystal (PhC) patterns in III-V semiconductor materials and more recently, the use of metallic structures. The dispersion characteristics in these fascinating materials can be used to control the propagation of very short pulses (fs) through photonic circuits. This work is part of the EPSRC funded Ultra-fast Photonics Collaboration (UPC), involving St Andrews, Bristol, Cambridge, Glasgow and Heriot-Watt Universities, and several industry partners. Our efforts cover both theoretical modeling, and fabrication and optical assessment of PhC structures. High quality PhC structures have been fabricated at Sharp Laboratories of Europe (SLE) Ltd. A typical structure (Fig. 2 (a)) is a 4.5µm ridge waveguide with local PhC patterns comprising holes of diameter 240 nm and ~1 µm depth, with lattice spacing of 420 nm. Optical characterisation of the samples involves recording the full scattering properties of the structure, i.e. trans(a)

mission, reflection and vertical scattering to provide an unambiguous verification of PhC effects. Of especial interest are the intrinsic losses of 2D PhC patterning (i.e. out-of-plane scattering) and the establishment of design techniques to reduce them. Theoretical studies have established suitable measures against which the performance and properties of a structure may be assessed. To demonstrate some of our techniques and capabilities we have recently examined the short pulse (100 fs to 10 ps) transmission properties of a zero-order 2-D metallic grating where the slits are seven times smaller than the incident wavelength. Significant transmission is possible in the narrow wavelength regions where the surface plasmon polariton (SPP) and waveguide mode resonances both occur. We showed that significant pulse delays can be achieved, e.g. 250 fs delay for a pulse width of 200 fs at the SPP resonance. In addition, the distance over which the time delay develops is much larger (ten times) than the actual longitudinal dimension of the grating structure and coincides with the distance over which the stored energy and the vortices of the Poynting vector extend (Fig. 2(b)).

(b)

Figure 2 (a): Passive GaAs/AlGaAs ridge waveguide with five rows of a 2D photonic crystal pattern. Holes have diameter 240 nm and depth 900 nm which penetrate through the entire guiding region (see inset). In transmission the structure suppresses TM polarisation (wrt TE) by 20 dB over the wavelength range 1.52 - 1.64 µm. (b): Pulse delay for the SPP resonance as a function of distance beyond the grating along with the variation in stored energy density at the SPP resonance. Solid lines: Absolute values of delay for several pulse widths. Dashed-dot line: The steady state stored energy density evaluated at the SPP resonance and averaged over a grating period.

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Quantum Optics ÒQubitsÓ and Optical Devices Based on Intersubband Transitions J. Dynes, M. Frogley, A. Green, H. Zervos, C. C. Phillips Intersubband transitions (ISBTs) occur between electrons confined in a semiconductor sample that is so small that the electron motion has been quantized in one or more dimensions. They give strongly peaked absorption spectra (which are rare in a solid) and behave essentially as "designer atoms". Because the wavefunctions, energies and symmetries of ISBTs can be controlled with great flexibility, they have substantial scientific and technological potential. Figure 3 shows the results of a quantum optical effect, arising from ISBTs, in a quantum well sample, which have been "dressed" with a laser pulse at one wavelength (124 meV photon energy), making the material transparent at a completely different one (the notch in the blue curve at 183 meV). If circularly polarized light is used, the strong ISBT absorption allows the spin quantum number of these electrons to be accessed optically. Placing the quantum well inside an optical micro-cavity then provides a versatile and practical means of combining cavity QED phenomena with the manufactuability and reliability of solid state devices.

Figure 3: Electromagnetically induced transparency in a quantum well ISBT absorption spectrum.

As an application example, we can use a "Quantum Cascade" diode laser, which operates with ISBTs, to make a simple 2-terminal device that will switch optical data from one wavelength to another. This is a critical requirement for all-optical data switching and routing and is attracting strong industrial interest. 12

Molecular Electronic Materials and Applications D. D. C. Bradley, A. J. Campbell, L. F. Cohen, P. G. Etchegoin, J. Nelson, P. N.Stavrinou Molecular Polymer Electronic Gain MediaMaterials for Optical and Amplifiers Applications and lasers G. Heliotis, R. Xia, M. Ramon, M. Campoy-Quilles, M. Pintani, M. Ariu, D. D. C. Bradley

of optical gain and loss properties for polymers with emission in the range 400 - 800 nm and (ii) fabrication and characterisation of lasers based thereon (Fig. 4). Organic Semiconductor Device Physics J. Nelson, D. Poplavskyy, R. Rawcliffe, A.J. Campbell, R.U.A. Khan, D. D. C. Bradley

Semiconducting (conjugated) polymers are an exciting new materials class for use in electronics and optoelectronics. In addition to many other applications, including full colour flat panel displays, there is strong interest in their potential as optical gain media for lasers and optical amplifiers. An important future target is the realisation of an electrically pumped polymer solid-state laser diode. Our programme focusses on (i) detailed characterisation

Fundamental research on the mechanisms of charge transport in organic semiconductors and the nature of contacts with metallic electrodes is essential to understand the behaviour of a variety of devices. Charge transport occurs by hopping between molecular sites in an energetically and spatially disordered landscape within which charge trapping may occur at interfaces, defects, impurities, or simply at the extremes of the density of states distribution.

(a)

(b)

(c)

(d)

Figure 4: (a) Spectral characteristics (absorption, photoluminescence and amplified spontaneous emission) of four polyfluorene polymers provided by the Dow Chemical Company (USA) that we have been studying as optical gain media. The emission from these materials allows access to the full visible spectrum (400-800 nm). (b) Typical 2-D "egg-box", 2nd order DFB laser grating (blue arrows indicate in-plane feedback and normal to plane outcoupling directions): Grating period L = 267 nm and depth = 30 nm. (c) The grating substrate was over-coated with a blue light emitting polymer, PFO film (dpolymer = 200 nm) to form a laser with state of the art performance. The laser emission was at 449 nm with a 7.8% slope efficiency and a threshold energy Eth = 0.8 nJ. (d) The emission beam was nearly diffraction limited with annular cross-section (central image) and azimuthal polarisation (peripheral images viewed through a linear polariser with axis shown by white arrows). This work was undertaken within the Ultrafast Photonics Collaboration.

We have a strong experimental and theoretical effort in this area. Experimental techniques include time-of-flight photocurrent and transient dark injection mobility measurements, current-voltage and impedance measurements, and electroabsorption spectroscopy, whilst theoretical techniques include Monte Carlo simulations of transport and recombination. One recent example of our work concerns dark injection experiments. We have shown that this method can be used to accurately measure the hole mobility in very thin films and that in materials where hole transport is non-dispersive, the mobility is independent of film thickness. This result is an important validation of the relevance of timeof-flight measurements on thicker (~1 µm) films, to photovoltaic and light emitting applications, where device thicknesses are typically 100 nm. A second example concerns the ability to achieve an ohmic contact with standard anode materials, a key requirement for both light-emitting devices and solar cells. This usually requires that the anode work function and polymer ionization potential be within 0.3 eV or less. We have, however, achieved ohmic hole injection even when DE ³ 0.6 eV, by means of an electrical conditioning step that modifies the interface. We have also evaluated a range of selfassembled monolayers of molecules with permanent dipole moments, as a simple means to raise the anode work function. Semiconducting polymer field-effect transistors (FETs) are a third example. Within the rapidly developing organic electronics field, polymer FETs have potential for use in a wide range of applications including radio-frequency identity tags, drivers for active matrix liquid-crystal and electrophoretic displays, and memory cards. Recent work has focused on ordered materials for high mobility FETs, new FET gate insulation materials, methods to lower the FET turn-on voltage using low ionisation potential polymers, and comparative bulk and FET carrier mobility measurements (Fig. 5).

as dye sensitised systems. In respect of dye-sensitised solar cells (DSSCs) we have studied in detail the recombination pathways that compete with photocarrier collection. An especial focus has been on solid state DSSCs where the electrolyte is replaced by a hole transporting organic semiconductor film. Our findings are now being integrated into a device model to better interpret the solar cell characteristics. In addition, electron transport is being modeled for films of quantumsized ZnO nanoparticles (collaboration with Debye Institute, Utrecht). The QDs behave like Ôsuper atomsÕ, with an electron-density dependent mobility that can be related to the filling of the quantised electronic levels. Our models will help to establish the conditions under which a conductinginsulating transition should be observed. Figure 5: (a) Source-drain current-voltage characteristics of a poly(9,9-dioctylfluoreneco-dithiophene) copolymer (F8T2) FET. (b) Comparison of the hole mobility calculated from the FET current-voltage characteristics and that derived from bulk space-charge-limited current diode and time-of-flight measurements for a poly(9,9-dioctylfluorene-co-phenylenediamine) (PFB) copolymer. The differences are believed to be due to the blocking behaviour of the source electrode, suggesting that polymer FET theory must be adjusted to take this into account.

Dye Sensitised nanocrystalline Oxide, Organic-Inorganic Hybrid and All-Organic Solar cells J. Nelson, F. M. Braun, R. E. Chandler, A. J. Chatten, S. A. Choulis, A. M. Eppler, Y. Kim, R. Pacios, D. Poplavskyy, P. Ravirajan, S. M. Tuladhar, D. D. C. Bradley Solar cells based on molecular materials rely on charge separation at the interface between electron acceptor and electron donor materials and 'distributed heterojunction' structures where the two phases contact over a large interfacial area are highly desirable. We are studying a range of these structures based on polymer/ polymer, polymer/molecule and polymer/nanoparticle blends, as well

A second research area concerns the PV properties of TiO2 / polymer nanocomposites. The polymer sensitises the TiO2 film, and affords high optical density with much thinner films than for solid state DSSCs, relaxing the demands on hole transporter conductivity. Very efficient charge separation occurs at the TiO2 / polymer interface with a factor of five increase in photocurrent quantum efficiency by insertion of a porous layer between dense TiO2 electrode and polymer (Fig. 6). Optimisation allows quantum efficiencies of 40% and power conversion (solar illumination) efficiencies ³ 0.6% (Fig. 6). This is more than double reported literature values and a systematic study is now underway to understand the remaining limiting factors. We have also undertaken a major research programme (funded by British Petroleum) focused on understanding and enhancing the efficiency of organic solar cells based on blends of C60 fullerene derivative PCBM and several conjugated polymers. PCBM is an effective electron acceptor and efficient electron transporter and we obtain power conversion efficiencies ³ 3% when blended with regioregular 13

Surface Enhanced Raman Scattering (SERS) R. Maher, P.G. Etchegoin, L. F. Cohen

Figure 6: (a) Device structure of hybrid polymer / TiO2 device. (b) Current density vs voltage characteristics of thin and thick polymer / TiO2 multilayer devices under simulated solar illumination (100 mW cm-2).

poly(3-hexylthiophene [P3HT] (from the Merck Chemical Company). We have characterised the key mechanisms of light harvesting, charge transport and recombination in such blends using a range of complementary techniques: These include device (JV and photocurrent quantum efficiency), time-of-flight and dark-injection mobility, photoluminescence quenching and electroabsorption spectroscopy measurements, and AFM studies of film morphology, as well as transient optical measurements of recombination kinetics (with Dr James Durrant (Chemistry)). Our results show that film morphology, especially in respect of the nature and length scale for phase separation, is critical to device function and the performance of P3HT:PCBM blends has been optimized accordinglyby solvent and annealing treatments. We have also developed a set of numerical models in order to interpret our experimental measurements in terms of the microscopic transport and recombination mechanisms, and to simulate and optimise light harvesting in thin organic films.

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SERS occurs due to huge enhancements of the local electromagnetic field at the surface of nanostructured metals such as gold, silver and copper in the presence of laser excitation. The SERS spectra of any particular analyte provide a strong chemical signature related to the adsorption of the analyte at the nanostructured metal surface, the details of the metalanalyte bond and also the resonant characteristics of the molecule itself. SERS may offer potential as an ultrasensitive chemical nose (winning out over fluorescence spectroscopy because of the vibrational information that it offers) but it is not yet sufficiently mature as a technology. Our work has focused on the fundamentals and applications of the technique, for example we have been investigating the origin of hot spots (locations that produce the largest enhancement). With the National Physical Laboratory we have been addressing metrology issues e.g. How do you compare different SERS surfaces? How do you conduct experiments that are reproducible? As part of this activity we have studied the ratio, r of the Anti-Stokes to Stokes scattering as a function of laser energy for the case of silver

Figure 7: Power dependence of r for the 1560 cm-1 Raman model of RH6G under 633 nm illumination at 300K. A feature resembling a threshold of stimulation can be seen. The value for r based on the predicted thermal value exp(-hwn / kBT), where wn is the frequency of the Raman vibration is also shown.

colloids and rhodamine dye molecules. If the Raman cross-section for the Stokes and Anti-Stokes signals are the same and the number of active molecules are known, r can be used to quantify the SERS enhancement factor. We find that r is a function of laser power and shows a threshold for stimulation. Transport and Magnetism A. D. Caplin, L. F. Cohen, J. Zhang Functional Magnetic Materials Y. Bugoslavsky, W. Branford, S. Clowes, L. F. Cohen, Y. Miyoshi, G. Perkins, S. Roy We are studying a range of highly spin polarised magnetic materials with the aim of using them as spin electrodes in the development of hybrid ferromagnetic-semiconductor devices for Spintronics. The magneto transport, Hall and Andreev spectroscopy of NiMnSb (in collaboration with FORTH in Heraklion, Crete) and Co2MnSi (in collaboration with the Materials Department at Cambridge University) yield information concerning the band structure and the integrity of the transport spin polarization. These key parameters vary as a function of composition, film thickness, grain size and strain. Understanding how to control and optimize them is critical to the success of device application. In 2003 we embarked on a new area, taking advantage of the versatility of the scanning Hall probe for large area imaging of magnetic materials. The work grew from collaboration with Dr Roy from Indore, who worked with us as an EPSRC Visiting Fellow. Using doped-CeFe2 alloys as "idealised" test-bed material systems we have been able to demonstrate conclusively that two features, phasecoexistence and metastability, must always be present at a disorderinfluenced first order transition. Through scanning Hall-probe measurements we were able to show extremely clear visual evidence of magnetic phase-coexistence on micrometer scales as the system is driven across the entire first order antiferromagnetic (AFM) to ferro-

was quenched by low applied field, which would have catastrophic implications for applications. We have clarified the situation and demonstrated that both gaps survive to the upper critical field (Fig. 9). We are just embarking on a major EU-funded project to further develop this material for conductors.

Figure 8(a): M versus T for 5% Ru doped CeFe2 in an applied magnetic field of 35 kOe after zero field cooling ZFC and field cooling FC. The AFM-FM transition region is highlighted and representative Hall-probe images have been inserted (each frame covers an area of 1 x 1 mm). The AFM state (black) is represented by field intensity less than 20% of the saturation value while yellow regions represent intensities greater than 20% of this value. At the onset of the transition FM-clusters appear at random positions across the sample and vary in size. The frame left of centre shows the effect of field cycling by 5 kOe after reaching 32 K in the FC path. Supercooled FM clusters are readily destroyed by this field cycling, highlighting the metastable nature of the magnetic state. (b) Images showing temporal evolution of the phasecoexistence at 20 kOe at 60K. Two images were taken 152 minutes apart, demonstrating nucleation and growth of the FM domains.

magnetic (FM) transition as a function of temperature, magnetic field and time (see Fig. 8). The simplicity of the CeFe2 system clarifies the underlying physics common to many classes of material that we now plan to study in particular magnetic shape memory alloys and giant magnetocaloric systems. Growth of Narrow Gap Semiconductor for Hybrid Sensor and Spintronic Applications W. Branford, S. Clowes, L. F. Cohen, B. Murdin, T. Zhang III-V Narrow gap semiconductors (NGSs) such as InAs and InSb are recognised to offer unique functionality for spintronic devices (i.e. devices that depend on the manipulation of spin rather than charge), because of their high effective g-factors, low effective mass and large spin-orbit coupling. Yet to date they have been relatively ignored compared to work on GaAs. We are involved in a European wide effort to exploit these properties by creating hybrid NGS Ð ferromagnetic metal devices. We have made significant progress towards producing high

mobility thin InSb material for hybrid sensors and, using a new Imperial recipe that minimizes dislocations, we have obtained films of unintentionally doped InSb on GaAs (100) with the highest room temperature mobility reported to date. Superconductivity: Fundamentals and Device Concepts

As well as the demand for higher speed/lower power devices, the newly developed concept of Ôquantum computingÕ has stimulated much work aimed at the fabrication of phase coherent quantum logic states or ÔqubitsÕ. Superconductors provide many possibilities due to their fast response times, low power dissipation levels and intrinsic macroscopic phase coherence. A particularly interesting class of device involves the controlled manipulation of quantised vortices within superconductors. Although the applications of such devices would be far-reaching, the key issue is how to produce the required vortex control. A novel solution could be to use the intrinsic interactions between Josephson vortices and pancake vortices that are known to co-exist in highly-anisotropic superconductors. Based on these concepts, we have initiated experimental studies into the new area of Flux Ratchet devices.

Y. Bugoslavsky, A. D. Caplin, L. F. Cohen, Y. Miyoshi, J. Moore, G. Perkins The simple binary compound MgB2, discovered to be super-conducting in 2001 with a Tc of 39 K, offers interesting prospects for applications, particularly for high current conductors and also perhaps Josephson junction device electronics. Our activities during 2003 have focused on the behaviour of the two superconducting gaps in the presence of magnetic field. We have been studying this fundamental aspect using tunnelling spectroscopy to look at how the density of states of quasiparticles and Cooper pairs evolve as a function of applied dc field. There had been a misconception that the smaller gap

Figure 9: The field dependence (D(B)) of the two energy gaps as determined by point contact spectroscopy for a MgB2 film with Tc = 38K .

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High Energy Physics Head of Group: Professor P. J. Dornan Members of the High Energy Group exercise significant influence in many of the current and future international experiments that investigate the fundamental particles and the forces between them. A primary aim is to address basic questions such as the origin of mass and the observed asymmetry between matter and antimatter. Much of the programme is directed at discovering where the Standard Model, that has proved amazingly successful in the description of electro-weak interactions, will break down, since theoretical expectations imply that it cannot be the final story. This will be accomplished by testing predictions to high accuracy and looking for phenomena outside the model such as supersymmetry and dark matter. CMS T. Virdee, G. Hall, C. Foudas, D. Britton, M. Raymond, C. Seez, J. Fulcher, G. Iles, A. Nikitenko, M. Ryan, R.Bainbridge, D. Colling, B. MacEvoy, H. Tallini

http://www.imperial.ac.uk/research/hep a hybrid photomultiplier device. A new amplifier for the ECAL readout system was developed at Imperial over the last year. The CMS tracker is a very large silicon detector system, which is an area where Imperial has two decades of expertise. Charged particle momenta are measured by bending in the 4T magnetic field, using finely segmented microstrip detectors read out with low noise, radiation hard CMOS chips (APV25) developed by Imperial College and Rutherford Laboratory, who are responsible for much of the electronic readout system.

Figure 1: The first section of the CMS solenoidal superconducting magnet coil. Behind it is the Forward Hadron Calorimeter (silver) and sections of the magnet iron yoke (red).

In the ECAL, electron and photon energies are measured by their interactions in lead tungstate crystals read out by avalanche photodiodes or vacuum phototriodes. We have been making precise measurements of the uniformity of the light collection along the length of the crystals using

An example of the type of discovery which CMS could make, other than the Higgs, is the search for evidence of extra spatial dimensions. The Randall Sundrum model postulates a 5D universe with two 4D surfaces (ÒbranesÓ). Fluctuations of the metric in the fifth dimension are described in terms of a scalar field, the radion (f), which can mix with the Higgs boson (h). This scalar sector of the model is parametrized in terms of Higgs and radion masses mh, mf, a dimensionless parameter, x, and the

The Large Hadron Collider (LHC), is a new CERN accelerator under construction due to begin operation in 2007. It will collide protons at centre of mass energy of 14 TeV and will be the highest energy machine in the world, opening a new window of discoveries in particle physics. In particular, it is expected that the elusive Higgs boson, which is the means by which quarks and leptons in the Standard Model obtain their masses, will be identified. The CMS (Compact Muon Solenoid) experiment, part of which is shown in Fig. 1, is a general purpose detector being constructed at LHC. Imperial College has major roles in detector design, construction and the scientific project management. The group is active in the electromagnetic calorimeter (ECAL), the charged particle tracking system and is developing software for detector readout and data analysis. 16

Figure 2: The di-photon (a), di-jet (b) and radion (c) reconstructed masses after all selections; (d) the 5s discovery contour in the (x-Lf) plane with 30 fb-1.

CP violation. Since then, using increased statistics, this measurement has been improved to better than 10% precision.

vacuum expectation value of the radion field, Lf. In certain regions of parameter space CMS could observe the radion via f ® hh when one Higgs boson decays into two photons and the other decays into a b-quark pair. As an example, the discovery reach in the plane of x and Lf, was evaluated for 30 fb-1 of data assuming mf = 300 GeV/c2 and mh =125 GeV/c2. In this region of mf and mh, f ®hh discovery will complement observation of a reduced f ® ZZ* rate compared to the Standard Model, confirming the nature of the observed intermediate-mass scalar. Event selections, in addition to those used for the h ® gg search, include the requirement to find two jets in the event with at least one of them tagged as a b jet. Fig. 2(a) and (b) show diphoton and the di-jet invariant masses after all selections for the background and for the signal at the maximal signal cross section point with 30 fb-1. Fig. 2(c) shows the reconstructed mass of the radion after cuts on the di-photon and the di-jet masses. The 5s contour in the (x-Lf) plane is in Fig. 2(d). D0 at the Tevatron R. Beuselinck, G.J. Davies, A. Goussiou, J. Hassard, J. Hays, R. Jesik, P. Jonsson The Tevatron, at Fermilab, near Chicago is the worldÕs highest energy particle accelerator, colliding together protons and anti-protons at close to 2 TeV, putting it at the very forefront of discovery. At a hadron collider the trigger (realtime selection of wanted events) is critical due to the very large QCD background. The highest level trigger at DÆ, Level-3, performs a partial reconstruction of the event (in ~100 ms) so placing it at the boundary between trigger and physics. The Imperial group is the largest single group at Level-3. Current activities include overall coordination and the development of track (and track based) triggers, including Ôb-taggingÕ algorithms, used to identify jets containing b-quarks. The output of such a tool is shown in Fig. 3; the signed Ôimpact parameterÕ

Figure 3: Signed impact parameter from a recent run, showing an excess of positive lifetime events.

from a recent run is displayed, showing a positive excess, indicating that bquarks are present in the sample. Another critical area is the understanding of the energy scale of the jets of particles produced after the proton anti-proton collision, and the optimisation of the jet mass resolution. Two of the main physics areas in Run II are B-physics and the search for the Higgs boson Ð the elusive particle that is responsible for giving mass to all we see around us. The Tevatron produces some trillion B mesons per year allowing us to study CP violation, rare decays and the way b and anti-b quarks mix. We have already produced significant results, including B-lifetimes; effort is now focused on B-mixing. Activity is also already well underway for the longer term goal of finding the Higgs. Within two years we will be able to answer whether LEP did see the first hints for a Higgs at around 115GeV. Increasing effort is going into SUSY Higgs searches, which rely heavily on b-tagging at the trigger level. BaBar W. Bhimji, D. Bowerman, P. D. Dauncey, U. Egede, I. Eschrich, J. Martyniak, G. Morton, J. A. Nash, D. J. Price The BaBar detector is located at the PEP-II electron-positron collider at the SLAC laboratory in California. The BaBar collaboration is studying CP violation using B mesons. In 2001 it made the worldÕs first observation of this phenomenon in B decays through the measurement of the parameter sin2b of the CKM matrix. This parameter is indicative of ÒindirectÓ

The Group is heavily involved in studies of CP violation in charmless hadronic B decays. These decays are sensitive to different CKM parameters, namely sin2a and g, and they should exhibit the ÒdirectÓ type of CP violation. This is expected to be rare and has not yet been observed in B decays; a significant observation would be very important and is the major goal of this study. An example of a computer reconstruction of a charmless B decay observed in the BaBar detector is shown in Fig. 4.

Figure 4: An example of a B decay candidate in the channel KKKS as observed in the BaBar detector. The thin blue lines show the reconstructed charged particle trajectories, the green blocks indicate electromagnetic energy in the calorimeter, the pink dots show detected Cherenkov light which is used to identify the type of particles and the large blue blocks indicate hits in the outer flux return chambers.

LHCb W. Cameron, P. Dornan, U. Egede, A. Howard, D. Price, D. Websdale, R. White The LHCb experiment is specifically designed to study B-mesons to the ultimate precision. The aim is to provide measurements of CPviolation with the highest sensitivity and to look for new physics beyond the Standard Model. For the CP-violation studies particle identification is required to identify the flavour of the quarks participating in the B-decay. Particles of a known momentum travelling through a medium with velocity greater than the speed of light in the medium emit 17

photons at a fixed angle depending upon the mass of the particle. By imaging the emitted photons onto a plane they will form rings where the radius identifies the mass of the particle. In LHCb this is done with two Ring Imaging Cherenkov Detectors, RICH1 and RICH2. To improve the projected performance of LHCb the experiment design went through a substantial re-optimization of its tracking and magnetic field configuration. This work was successfully finished in 2003 and the new experiment design can be seen in Fig. 5. The implications for the RICH1 detector were large and the Imperial Group is responsible for turning the redesign into a full design that satisfies demanding criteria.

Figure 5: The layout of the redesigned LHCb experiment. The main involvement for Imperial is the design and construction of the RICH1 detector.

ZEUS C. Foudas, A. Jamdagni, K. Long, A.Tapper The HERA collider in Hamburg is a microscope used by the ZEUS collaboration to look deep inside the proton. A 27.5 GeV electron collides with one of the quarks inside a 920 GeV proton, splitting the proton and throwing out debris that can be detected. The proton structure is studied together with the nature of the strong force. The Group has provided key pieces of ZEUS, which it helps run and maintain. From summer 2003 HERA has been running with high intensity polarised positron beams. This has allowed us to make the first ever measurements of the polarisation dependence of the charged current cross sections. We plan also to measure the polarisation dependence of the neutral current cross section and to use these 18

measurements to search for physics not described by the SM. Crucial to this programme is a precise measurement of the lepton beam polarisation. IC physicists have taken the lead in the development of a position detector that will allow the required precision to be obtained. Neutrino Experiments E. McKigney, M. Ellis, A. Jamdagni, K. Long, P. J. Dornan, W. G. Jones The discovery of neutrinos changing from one type to another as they travel through space (Ôneutrino oscillationsÕ) implies that neutrinos are massive, that the Standard Model is incomplete and makes the neutrino sector the only presently accessible window on physics beyond the Standard Model. The small, but non-zero, neutrino mass has astrophysical consequences. In particular, the interactions of the neutrinos may underpin the mechanism by which antimatter was removed from the early universe. The far-reaching consequences of neutrino oscillations justify a dedicated experimental programme. The worldwide consensus is that a Neutrino Factory Ð an intense high-energy neutrino source derived from the decay of a stored muon beam Ð is the ultimate tool for the study of neutrino oscillations. We have begun an ambitious programme of R&D aimed at developing a conceptual design for the Neutrino Factory. To reach the required stored muon intensity requires that the size and divergence of the muon beam be reduced or ÔcooledÕ. The technique that has been proposed to do this involves passing the muon beam through liquid hydrogen, which reduces the beam energy, and then reaccelerating the beam. This sequence of operations cools the beam and is referred to as Ôionisation coolingÕ. In order to demonstrate the feasibility of ionisation cooling, we are mounting the Muon Ionisation Cooling Experiment (MICE). We proposed the scintillating fibre tracker that forms the baseline instrumentation for the MICE spectrometers. Over the past year we successfully built a prototype tracker which is shown in Figure 6.

Figure 6: Prototype scintillating fibre tracker prior to installation in aluminium support tube.

A crucial input to the MICE experiment is the precise measurement of the scattering distributions of muons as they pass through matter. We have played a leading role in the MuScat experiment that will measure these distributions. Over the coming year we plan to expand out activities in the Neutrino Factory area. We have forged a close collaboration with CCRLCÕs Rutherford Appleton Laboratory to study the conceptual design of the accelerator complex and to develop accelerator structures for the highpower pulsed proton injector. Calice D. Bowerman, W. Cameron, P. D. Dauncey, D. J. Price, O.Zorba There is a large worldwide effort working towards a high energy electronpositron linear collider with a centre of mass energy in the range 500-1000 GeV. Such a linear collider would allow precision measurements of any Higgs (or SUSY) particles in this mass range as well as having a significant discovery potential of its own. To fulfill the physics potential of this machine, the calorimetry for a detector at the linear collider needs to be able to reconstruct jet energies with resolutions exceeding anything previously achieved. The Calice collaboration has been formed to study both electromagnetic and hadronic calorimetry for a linear collider detector. The Imperial group has led the design of the readout electronics for a prototype highgranularity electromagnetic calorimeter within this collaboration.

Laser Consortium Director: Professor J. P. Marangos The Blackett Laboratory Laser Consortium researches new frontiers of science made possible by high power ultra-short laser pulses. This exciting area of science includes new developments in ultra-fast measurement, generation and applications of attosecond duration light pulses, controlling quantum processes in molecules, producing bright sources of radiation in the X-ray region and creating high energy density plasmas. We operate three high power lasers; a high energy sub-picosecond glass system and two titanium:sapphire systems; one delivering up to 100 mJ in a 50 fs pulse at a 10 Hz repetition rate, and a second 1 kHz repetition rate system with 30 fs duration ~1 mJ pulses. Using these lasers and through our accompanying theoretical work we are making pioneering contributions to the fields of ultra-short pulse generation, non-linear optics, plasma physics, and molecular dynamics. We are funded with support from the EPSRC/MOD, the Basic Technology Programme of the RCUK and through various grants from the EU and the Royal Society. There are active collaborations with other leading groups in Europe and North America. The Blackett Laboratory Laser Consortium forms part of the Quantum Optics and Laser Science Group. Strong Field Theory Forest fires and cluster ionisation in strong fields. P. L. Knight, L. Gaier, L. Chipperfield. In a collaboration with the group of Paul Corkum at NRC Ottowa, we investigated the ionisation of clusters by short, intense laser pulses. Traditionally, the dynamics of laserinduced breakdown is divided into several stages. First, conventional multiphoton ionisation provides a seed population of free electrons. Second, these electrons take energy from the field through laser-assisted collisions. Third, when the electron energy exceeds the bandgap, electrons

http://www.qols.ph.imperial.ac.uk/consort/

are promoted into the conduction band. Clearly, this picture should change when dealing with extremely short - few cycle laser pulses: at some point the pulse duration should become too short to enable significant heating of the electrons in the conduction band. Where this boundary lies depends on the laser wavelength, intensity, bandgap, etc. Very large atomic clusters are similar to dielectrics for short laser pulses, as long as the expansion of the cluster is negligible during the pulse. Mechanisms of damage in dielectrics are thus similar to ultrafast cluster ionisation, and act at very early time. They are complimentary to the ionisation and absorption mechanisms induced by the cluster expansion. We have concentrated on one such damage mechanism which becomes operative when the laser pulses are too short (and the intensities and/or energies too low) to induce traditional avalanche ionisation. Mathematically, this mechanism can be described as the propagation of Òforest firesÓ. The core effect responsible for laserinduced Òforest firesÓ in clusters and dielectrics is known as Òenhanced ionisationÓ in molecules and Òionisation ignitionÓ in clusters. When electrons localise on the nuclei (e.g. during dissociation of a molecule, or in a rare gas cluster), removal of such an electron leaves an uncompensated positive charge - a hole. We describe the dynamics of ultrafast damage in dielectric materials irradiated by light below the conventional breakdown threshold. The damage occurs on a sub-laserwavelength scale. It starts with the formation of nano-droplets of plasma which grow like forest fires, without any need for heating of the electrons promoted to the conduction band. The dimensionality of the damaged area can be fractal and changes during the laser pulse. This mechanism is operative in both rare gas clusters and dielectrics interacting with ultrashort, moderately intense laser pulses which include only a few periods of the driving field, too fast for traditional

avalanche mechanisms.

Figure 1: Numerical modelling of electron dynamics driven by a single cycle pulse.

Laser Development and modelling Modelling of Few-cycle OPCPA lasers, G. H. C. New. Chirped Pulse Amplification (CPA) is an elegant solution to the problem of non-linear optical damage in high power lasers. However current CPA lasers are limited to durations > 25 fs by the finite gain bandwidth of materials such as Ti:sapphire. Optical parametric chirped pulse amplification (OPCPA) has advantages over ÒtraditionalÓ gain media in terms of both bandwidth and amplified spontaneous emission (ASE). OPCPA uses non-linear optical processes to transfer energy from a pump to a seed pulse in a single pass through a non-linear crystal. This provides up to 5x the bandwidth of Ti:sapphire, single pass gains approaching 105 and greatly reduced ASE. A split-step code has been developed in collaboration with Ian Ross (RAL) that solves the coupled wave equations with dispersion to all orders. The code allows for three OPCPA stages, 19

and can handle a dynamic range between uncompressed and compressed pulse widths of > 105. It incorporates stochastic features including non-transform limited pulses and random noise. Using this code we have studied a range of OPCPA designs to guided the construction of a new laser system able to deliver a sub-10 fs pulses at an energy of >10 mJ and focused intensities >1018 Wcm-2. Shaping of High Intensity Laser Pulses J. P. Marangos, R. A. Smith, J. W. G. Tisch, K. Mendham, J. Robinson, A. Moore. The frequency components of an optical pulse can be dispersed and recombined in a so called Ònull stretcherÓ. By placing a modulator in the Fourier plane of the stretcher these wavelengths can be individually manipulated, allowing detailed control of the temporal shape of a high power laser pulse. We have recently implemented such Òpulse tailoringÓ on our high power Ti:Sapphire laser system using a multi-element LCD array. This allows us to created pulses with variable duration, chirp and temporal structure. The pulse shaper is coupled to a Genetic Algorithm through a feedback loop allowing the laser to ÒlearnÓ about and optimise experiments in situations where the ÒbestÓ laser pulse is unknown. Diagnostics such as a Frequency Resolved Optical Gating Spectrometer (FROG) then allow us to determine the pulse shape found experimentally. We have recently used this technique to optimise x-ray emission from a cluster gas (Figure 2).

Laser Development Attosecond Project and modelling J. W. G. Tisch, J. P. Marangos, R. A. Smith, J. Robinson, C. Haworth, P. Bates. September 2003 saw the start of a substantial new project to produce, characterise and apply attosecondduration light pulses (an attosecond is 10-18 s). Funded by the Research Councils UK through the Basic Technology Programme, this is a collaborative project centred and managed within the Laser Consortium, involving Birmingham, Oxford, and Reading universities, UCL, and the CCLF at RAL.

Figure 4: Spectra of pulses from the hollow fibre. Black curve is with fibre evacuated (essentially the input laser spectrum); the red curve is with 2 bar of Argon in the fibre.

energetic collisions with their cores. Important steps towards the production of the intense, few-cycle pulses required have already been taken in a new SRIF refurbished Laboratory. We use a gas-filled hollow waveguide in which femtosecond laser pulses are spectrally broadened by SPM and recompressed using chirped mirrors to the few-cycle limit. By coupling 0.6 mJ, 25 fs pulses centred at 800 nm from a commercial, kHz laser into a 1 m long gas-filled 250 mm diameter hollow fibre (shown in Fig. 3) we have demonstrated the necessary spectral broadening to support fewcycle pulses. Bandwidths > 300 nm have been demonstrated (see Fig. 4) at input intensities of » 1014 Wcm-2 with energy transmission > 60% and an extremely high quality guided mode. Work is now underway to compress these pulses to < 6 fs. Related developments to produce high power sub-femtosecond pulses

Figure 3: Gas-filled hollow fibre used to spectrally broaden fs pulses.

The attosecond source at Imperial College is based on non-linear frequency conversion of intense (~1015 Wcm-2) ultra-fast (~6 fs) near-IR light pulses in gaseous media through high harmonic generation.

Figure 2: FROG Image of a double pulse evolved using the genetic algorithm to optimise the soft x-ray yield from Xe clusters.

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Attosecond XUV bursts of light are produced as electrons in the medium are first dragged away from their ion cores, accelerated in the strong laser field to around 100 eV, and then half a cycle later make single,

Figure 5: The grey spectra shows the advantage of driving with two Raman resonant fields. Insert:. Calculated temporal profile of the pulse that could be synthesized from this spectrum.

have been made using high order Raman side band generation. In these experiments high pressure molecular gases confined in a hollow fibre are driven by a pair of 100 fs laser pulses tuned to Raman resonance. The result is very efficient high order side band generation producing bandwidths able to support pulsesMolecules under 1 fsin(see Fig.fields 5). strong J. P. Marangos, E. Springate, R. DeNalda, E. Heesel, N. Kajumba. We have used techniques pioneered at Imperial to study strong field interactions with controllably aligned molecules. A 300 ps pulse from the Ti:S CPA laser was used to perform non-resonant adiabatic alignment in rotationally cooled (Trot~20K) molecules (e.g. CS2, CO2). These aligned molecules were then exposed to intense 70 fs pulses focused to » 1014 Wcm-2 and the dependence of HHG (high harmonic generation) studied. The origin of alignment effects on HHG has been found to arise through anisotropy in the phase and amplitude of the harmonic dipole, a feature unique to molecules. We have examined the dependence of HHG yield upon the angle between the molecular axis and laser polarisation. Recent data (15th harmonic from aligned CO2) illustrating this is shown in Fig. 6. Harmonic emission is found to be lower in CO2 molecules aligned parallel or perpendicular to the laser field direction and to be larger for intermediate angles. This has been well reproduced in calculations that take into account the antisymmetric orbital symmetry of the

Figure 6. Dependence of HHG yield on the angle between E-field and molecular axis.

relevant electronic states in the molecule. This indicates that quantum mechanical destructive interference between regions of the original wavefunction that have different sign leads to suppression of HHG. More recently we have begun experiments that move beyond the adiabatic alignment process and employ impulsive alignment, giving strong alignment under field free conditions. An example of a rotational revival measured using an optical probe is illustrated in Fig. 7. This method is now being applied to the study of aligned molecules in intense fields.

Figure 7: A rotational revival in impulsively aligned CO2 measured using polarisation rotation.

High intensity laser interactions with nanoparticles

Figure 8. Evolutionary ÒFitness curveÓ for large laser irradiated Xe clusters showing more than 100% improvement in absolute x-ray yield.

We have also continued our work on shaped blastwaves produced in laser machined cluster media. Atomic clusters are extremely efficient absorbers of intense laser light and we use them to create ultra-high energy density ( >5x105 J/cc) plasmas. Energy initially deposited by the laser in a narrow 20 mm cylinder propagates outwards as a Mach 40 shockwave, heating and ionising the surrounding cold material. Figure 9 shows experimentally measured blastwave radii for a range of cluster gasses, from which we determine the Òdeceleration parameterÓ that characterises the blastwave evolution.

R. A. Smith, J. W. G. Tisch, J. Marangos, D. Symes, E. Springate, A. Moore J. Robinson, J. Lazarus. Optimisation of the yield of soft x-ray emission from laser irradiated 350,000 atom cluster targets between 10400 eV was investigated using highpower pulse tailoring. Our Ti:Sapphire laser was coupled to a pulse shaper to produce 10 mJ, 90 fs pulses which were focussed into a cluster jet. The x-ray yield from the clusters was then fed back to a genetic algorithm controlling the pulse shaper.

Figure 9. Blast wave radius as a function of time for laser irradiated H, Ar and Xe cluster plasmas showing non Sedov-Taylor behaviour.

The algorithm searched for optimum x-ray generation by evolving the pulse into a multi-bunch structure as shown in Fig. 2. Figure 8 shows a fitness curve for a ten generation evolution experiment demonstrating an improvement of more than 100%. 21

Photonics Head of Group: Professor P. M.W. French The broad themes of research are imaging and sensor technology, fibre and laser optics and biophotonics. Current projects include adaptive optics applied to astronomy and medical (ophthalmic) imaging; biomedical optics, including highspeed 3-D imaging and fluorescence lifetime imaging applied to tissue diagnosis and molecular biology; rigorous electromagnetic theory (FE, FDTD, volume integral methods), applied to focusing, imaging and polarisation, chiral media and Bragg structures; high power fibre laser technology, including telecommunications amplifiers and sources, nonlinear fibre optics and compact high power visible/UV sources; optical fibre sensors, high power solid-state laser technology and nonlinear optics; ultrafast diode-pumped solid-state and fibre laser technology and optical storage, including DVD, multiplexed high density storage. A representative selection of topics is given below: Optical Fibre Laser Technology S. Popov, J. R. Taylor Our research, which builds on high power fibre amplifier technology and our continued interaction with IPG Photonics, the world leader in this technology, continues to emphasise applications outside telecommunications. We have developed a novel self-starting source of ultrashort pulses, which exploits polarization and spectral shaping, together with high single pass gain, in normally dispersive, Yb-doped fibre lasers to provide pulses of durations selectable in the range of 1-20 ps. Emphasis has been placed upon schemes. In a cooperative research programme with IPG these pulses have been amplified to peak powers of 60kW at an average power of 9W. In the past year, considerable research effort has been directed towards fully fibre integrated chirp pulse amplifiers 22

http://www.imperial.ac.uk/research/phot using air-cored photonic band gap fibre, where the air core reduces the effect of non linearity and the spectrally selective transmission characteristic of the band gap adjusts the overall dispersion to be anomalous in specific spectral regions. As a consequence, we have demonstrated the worldÕs first all fibre chirp pulse amplifier, achieving peak powers of 20 kW at multi-watt average powers. Pulse compression up to 100 times has been achieved in all fibre configurations with chirped pulses amplification in Yb, Yb:Er and (at unrestricted wavelengths) Raman fibre amplifiers. Exploiting our capability of low loss splicing of photonic crystal fibres to conventional fibres, we have developed low maintenance broadband continuum sources under c.w. operation utilizing both conventional highly nonlinear fibre and holey fibre. In conventional fibre, a flat spectral continuum extending from 1.5-2.1 mm was achieved, with less than 1 dB peak to peak ripple and a spectral power density of 16 mW/nm. In holey fibre, pumped at 1 mm, a >5W c.w. continuum extending over 300 nm has been obtained, which has been demonstrated, in collaborative experiments at MIT, to replace conventional solid state laser technology for in vivo Optical Coherence Tomography. Sculptured Thin Films M. W. McCall Sculptured Thin Films are formed by vacuum deposition of vaporised material onto a substrate that moves in a periodic fashion during growth. For a rotating substrate a chiral morphology results in which the material forms into helicoidal columns (Fig. 1). Chiral sculptured thin films have some promise for various sensing and filtering operations, as their properties are selective to circularly polarised light. Our recent research has shown how chiral mirrors can be used to design a circularly polarised resonator Ð see Figure 2.

Figure 1. Scanning electron micrograph of a chiral sculptured thin film (courtesy of Pennsylvania State University).

Figure 2. (Upper) Open cavity handed resonator formed using a pair of chiral mirrors. (Lower) Spacerless handed resonator.

Nonlinear Optics and Laser Technology M. J. Damzen We are developing a range of laser and nonlinear optical technology, including novel high power solidstate laser devices for applications ranging from industrial processing to medicine, laser displays and remote sensing. Novel diode side-pumped solid-state designs operate at high output power levels (to 100 W and beyond) with ultrahigh conversion efficiencies (60%-70%), producing world-record power levels at some laser transitions. By incorporating these sources with nonlinear frequency conversion we are developing new compact efficient sources at high average power (multi-watt) in the red, green, blue and UV spectral regions for biomedical and laser display applications. One of the key problems to scaling the power of solid-state lasers are strong heating effects in the

Figure 3: Self-adaptive diode-pumped Nd:YVO4 laser is created by formation of a holographic grating within laser amplifier. The grating encodes and corrects for severe intracavity distortion to maintain high spatial quality output beam.

laser amplifier leading to thermallyinduced lensing and stress-induced birefringence that degrade beam quality and reduce stability and efficiency of the laser. We have pioneered a range of nonlinear techniques to provide lasers that self-organise to automatically correct these adverse effects, including a new self-adaptive solidstate laser systems that maintain the laser efficiency and output beam quality, based on a novel dynamic holography process within the laser amplifier itself. Such c.w. diodepumped solid-state lasers with adaptive resonators operate at many tens of watts with diffraction-limited beam quality. More recently, we are developing adaptive interferometers for a range of real-world applications including remote ultrasound detection for non-destructive testing, medical biomechanical health and free-space optical communications and remote sensing. A programme to characterise new nonlinear optical media complements the work on nonlinear optics. As well as including the conventional bulk nonlinear crystal media such as KTP and periodically poled KTP, we have developed investigation and application of photorefractive media that have strong nonlinear effects even at low light levels < 1 mW. For future nonlinear materials in information processing and sensors, we are also initiating a new nanotechnology programme to study nonlinear optical properties of biological micro-

tubules (and carbon nanotubes). High Resolution Imaging of the Human Retina using Adaptive Optics C. Paterson, G. T. Kennedy, J. Massa, C. Walker For ground-based astronomy, adaptive optics provides a remarkably effective solution to problems due to aberrations arising from atmospheric turbulence and associated random changing refractive index fluctuations. The principle is to measure the aberrations on light from a known object (such as a guide star) using a wavefront sensor and then to correct for them in realtime using for example a dynamic deformable mirror. We are applying the same principles to a range of biomedical and industrial applications and are particularly interested in imaging the human eye, in which aberrations may arise from a number

of sources including static aberrations in the cornea and lens and dynamic tear-film fluctuations. Imaging the retina is important medically since the blood vessels in front of the retina give a unique unobscured view of a complete section of the cardiovascular system - offering enormous potential for disease diagnosis and monitoring. Usually individual photoreceptors are too small to be imaged but they may be observed if the pupil is dilated and the aberrations of the eye are corrected. We are working with ophthalmologists to apply adaptive optics to imaging of neonatal retinas for the detection of retinal disease and for studying the process of visual development. We are also applying adaptive optics to correct for strong atmospheric turbulence, with potential for imaging, remote sensing and communication. This work includes atmospheric modelling and characterisation applied to beam propagation and to multiconjugate adaptive optics - a technique using multiple correction mirrors to increase the field of view of imaging systems. As the atmospheric turbulence effects increase (e.g. over long optical propagation distances), scintillation and phase dislocations or optical vortices also appear, which present enormous challenges to adaptive compensation and for which we are developing new wavefront sensing and correction techniques. We have also started a programme in which we are fabricating our own adaptive optics components - including deformable mirrors, wavefront sensors and control, specifically to address these promising applications. Electromagnetic Focusing and Imaging and Applications to Optical Data Storage, Microscopy and Sculptured Thin Films P. Tšršk

Figure 4: Confocal scanning ophthalmoscope retinal image

We are researching various means to achieve much improved optical storage capacity, including super resolution techniques by means of transfer function equalisation, superresolving filters and multilevel coding, aiming to exploit the maximum information content by unit area that is possible to store on an optical disk. 23

has focused on high-speed widefield image acquisition, offering sub10 ps temporal discrimination for wide-field functional imaging of chemical and biological samples, contrasting different chemical species and different fluorophore environments. We combined FLIM with multi-spectral imaging and optical sectioning to realize 5D fluorescence imaging and have adapted FLIM to polarization anisotropy to image rotational diffusion dynamics. Recently we have demonstrated real-time (15 frames/s) FLIM applied to endoscopes and multi-well plate reader systems. Figure 5: Light scattered by a DVD track

Accordingly we have developed a complete set of analytical/numerical modelling tools Ð which may also be applied to optical imaging systems. Interaction of light with either the surface of a CD/DVD or any other complex specimen is considered via rigorous electromagnetic solvers. We have developed high angle Finite Difference Time Domain (FDTD) and Volume Integral solvers. As a result of our research it is possible to optimise model performance. Our technique, which is able for the first time to combine analytical and numerical techniques is, to our knowledge, the most accurate way of modelling optical microscopes, optical data storage devices and other optical systems for metrology. To maximise our numerical capabilities we have built a computer cluster possessing 36 nodes, each with 2.4 GHz CPU and in total 36 GB memory. This has been used to model how light is scattered by a surface element of the next generation of DVD disks (shown in Fig. 5) illuminated by a semiconductor laser (on the left) and the intensity of light scattered by the individual data pit (on the right). Our model can provide the distribution of the electric field or intensity at the detector, the detector signal and jitter information, etc. Our research also includes the development of methods that are capable of producing an arbitrary polarisation structure in the vicinity of focus of high numerical aperture lenses. We take a combination of 24

vectorial Gauss-Laguerre and Gauss-Hermite beams as orthogonal basis functions and we use them to expand a Ôwish functionÕ describing the polarisation structure in question. This research has great use in optical data storage, ellipsometry and polarised light optical microscopy. Functional imaging for biology and medicine P. M. W. French, I. Munro, M. Neil, F. Reavell We continue to apply ultrafast and tunable laser technology, including compact diode-pumped all-solid-state and fibre laser sources, to novel imaging applications with a strong emphasis on multi-parameter fluorescence imaging for clinical diagnosis, molecular biology and drug discovery. Our main programmes are high speed 3-D coherence gated imaging and fluorescence life-time imaging (FLIM). The 3D imaging programme builds on our invention and development of low coherence photorefractive holography for high speed depth resolved imaging, including through scattering media, with an inherent rejection of d.c. (diffuse light) background. The use of photorefractive GaAs/AlGaAs MQW devices, in partnership with David Nolte at Purdue University, has realized wide-field depth resolved imaging at ~ 500 frames/ second. Other techniques for widefield optical sectioning include low coherence interferometric imaging with direct CCD detection and structured illumination. Our FLIM programme

We have also established a confocal scanning/multiphoton microscope, broadly tunable ultrafast laser/OPA technology and a multi-beam, multiphoton microscope that provides widefield optically sectioned images at video rate, which has been combined with hyperspectral and polarisation resolved imaging as well as FLIM. In collaborations with colleagues in the Bioengineering, Biology, Chemistry Departments and the Faculty of Medicine, we are applying our unique instrumentation to molecular biology (applying FLIM to genetically expressed probes such as EGFP, to report both the localization and local environment of target proteins), to medical applications (using FLIM to provide intrinsic autofluorescence contrast in unstained tissue samples, with potential diagnostic applications) and to drug discovery (using multi-parameter fluorescence imaging to develop label-free assays).

Figure 6: Intrinsic FLIM contrast of unstained (rat) tissue.

Plasma Physics

http://www.imperial.ac.uk/research/plasma

Head of Group: Professor K. Krushelnick The Plasma Physics Group conducts research on both astrophysical and laboratory plasmas and is the largest university based plasma physics group in the UK. We are involved in fusion energy research and do both experimental and theoretical work on magnetically confined fusion plasmas (in collaboration with UKAEA Culham) and on inertial confinement fusion using the MAGPIE z-pinch facility in Blackett Laboratory and the high power laser facilities at the Rutherford Appleton Laboratory. Magnetic Confinement fusion experiments and theory S. Cowley, G. Turri, N. Joiner, D. Applegate, M. Coppins, A. Meakins, F. Lott, J. Paley, O. Keating, J. Martin MAST, the MegaAmpere Spherical Tokamak, is an experiment operated at the Culham Laboratory in Oxfordshire. This acronym underlines two main features of this device: the plasma current achieved is greater than 1 MA and the design is non-conventional, i.e., the aspect ratio is small such that the major and minor radii are comparable in size. Our Group is studying the studying magnetic reconnection in the central core of these plasmas both theoretically and experimentally. Of particular

remnant. We have shown that the large CR flux dominates the dispersion relation and produces a new kind of strongly driven mode which rapidly becomes non-linear and generates magnetohydrodynamic turbulence.

Figure 2: Gyrokinetic simulation of MAST

interest is the MHD ÒsnakeÓ instability (because of soft x-ray (SXR) traces obtained from the diagnostic system, see Fig. 1) which is due to reconnection of magnetic field lines in the core plasma. Plasma instabilities on the scale of the ion and electron gyro-radius (micro-instabilities) are also studied using gyro-kinetic simulations. Simulations are performed using a code that utilises magnetic flux following geometry because the most computationally efficient simulation domains are thin tubes (flux-tubes) which follow the magnetic field lines (see Fig. 2). Microinstabilities are thought to be the source of fine scale plasma turbulence. Cosmic ray acceleration and magnetic field generation A. R. Bell The theory of cosmic ray (CR) acceleration to energies of 1015 eV by diffusive shock acceleration in supernova remnants (SNR) is well established. As a SNR shock expands into the interstellar medium, CR are confined in the shock environment by scattering off magnetic field fluctuations receiving a succession of kicks as they are repeatedly overtaken by the shock.

Figure 1: Typical SXR data obtained when snake instability develops

The turbulence stretches the magnetic field lines, thereby increasing the magnitude of the magnetic field, decreasing the CR gyroradius, and making CR acceleration to higher energies possible (see Fig. 3).

However, the standard theory cannot account for CR energies beyond 1015 eV because the CR gyroradius in a typical interstellar magnetic field exceeds the radius of the supernova

Figure 3: Magnetic field line before and after stretching by cosmic rays.

Wire array Z-pinch implosions S.V. Lebedev, J. P. Chittenden, S. N. Bland, S. C. Bott, D. J. Ampleford, C. A. Jennings, J. Rapley, M. Sherlock, M. G. Haines The intense bursts of soft X-ray generated by fast plasma implosions are used for Inertial Confinement Fusion research. The physics of imploding plasmas formed from cylindrical arrays of fine metallic wires are studied on the 1.5 MA MAGPIE pulsed power facility. One of the critical parameters controlling the implosion dynamics is the rate with which the plasma is formed from the ablating wires. We have found that

Figure 4: Rapid increase of ablation rate for the gaps below ÒcriticalÓ

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the ablation rate strongly depends on the magnitude of the magnetic field pushing the plasma towards the array axis. The observed dependence of the ablation velocity on the inter-wire separation (Fig. 4) may explain the existence of the optimum wire number maximizing the radiation power. We use 3D resistive magneto-hydrodynamics simulations to investigate factors limiting X-ray power production in imploding wire arrays. Figure 5 shows the broken plasma structure originating from sixteen aluminium wires in a MAGPIE wire array, imploding under the jxB force and converging on axis. The peak X-ray power is found to be limited by a combination of 3D asymmetry, self trapping of the radiation flux and a reduction in the current delivered to imploded pinch caused by the trailing mass. Simulations of different wire array configurations reveal the mechanisms by which the X-ray power can be increased.

ation phenomena in this regime of laser-plasma interaction using a Fokker-Planck simulation code called IMPACT. In particular, we are looking at how electron transport and magnetic field generation change under these 'nonlocal' conditions. As well as being of fundamental interest, this situation is relevant to indirect drive ICF. Here the conditions in the (ionized) gas-fill and near the walls of hohlraums (i.e., gold, black body X-ray cavities) are far from 'local'. How non-local effects influence the evolution of this system is still an open question. Previously it was known that (without a magnetic-field) thermal transport is not adequately described by the conventional `Braginskii' theory when the mean-free-path becomes large: the heat flow cannot simply be related to the instantaneous, local temperature gradient and plasma conditions. We have shown that non-local effects are important to magnetic field generation. Laser-solid interaction at ultra-high intensity A. R. Bell, A. P. L. Robinson, R. J. Kingham

Figure 5: Density surfaces from a 3D simulation of a 16 wire aluminium wire implosion.

Transport and B-field generation in nanosecond laser-plasma interactions R. J. Kingham, A. R. Bell, M. G. Haines The physics of the interaction of nanosecond laser pulses with plasma is relevant to inertial confinement fusion (ICF) plus other applications such as X-ray lasers. At these intensities (1013 Ð1016 W/cm2) strong non-equilibrium effects are prevalent and a kinetic (rather than hydrodynamic) description of the interaction is required. We are investigating the underlying transport and magnetic-field gener26

Irradiation of solid targets by high intensity, sub-picosecond laser pulses efficiently produces electrons, ions and photons with MeV energies. We are investigating the underlying laser-solid interaction processes using a Fokker-Planck simulation code called KALOS. The absorption of laser light at the target surface directly generates energetic electrons which stream into the target. To maintain charge balance, the current of energetic electrons must be balanced by an opposite 'return current' of thermal electrons. When the beam of energetic electrons reaches the rear surface of the target the electrons emerge into the vacuum setting up an electric field which reflects most of them back into the target and at the same time draws energetic ions out into the vacuum. We have reached a point at which

electron beam propagation through the solid is reasonably well understood, and we are investigating the complicated structures in particle density, ionisation state and electric field occurring at the rear surface of the target which cannot be adequately modelled with any other codes. Laser produced plasmas as a compact particle accelerator Z. Najmudin, K. Krushelnick, A. E. Dangor, M. Tatarakis, B. Walton, S. P. D. Mangles, M. S. Wei, E. L. Clark, A. Gopal, C. D. Murphy, A. G. R. Thomas. The large electric fields at the focus of high power laser systems can accelerate particles to high energy in extremely short distances. In recent experiments, we have used several laser systems to investigate laser acceleration mechanisms. The Petawatt laser at RAL can be focused to intensities approaching 1021 Wcm-2 with an associated electric field of almost 1013 Vm-1. By focusing into a plasma, the transverse motion of electrons in the laser field can be randomised into a longitudinal motion. This allows the electrons to travel with the laser pulse, experiencing further acceleration. In our experiments, we have recorded electrons accelerated by this mechanism with energies up to 350 MeV Ð the highest recorded from such an interaction. The Astra laser system is a much more compact laser system, providing up to 0.5 J laser pulses but now in t Å 40 fs laser pulses. These ultrashort pulses are more efficient at generating plasma wakefields which also have extremely large longitudinal electric fields, and

Figure 6: Simulation of PetaWatt laser interaction showing the importance of propagation instabilities

can accelerate electrons to high energy. Indeed, the breaking of these waves can themselves provide the electrons to be accelerated. We have found that close to threshold for this ÒwavebreakingÓ process, only a small bunch of electrons is accelerated. This results in very short duration bunches with greatly reduced energy spread which is important for the development of future electron accelerator technology. X-pinch Simulations and Experiments A. Ciardi, J. P. Chittenden, K. Krushelnick, A. E. Dangor, F. N. Beg An x-pinch consists of two or more thin metallic wires crossed in the shape of an ÒXÓ. By applying a large fast rising current through the wires, several rapid bursts (< 1 ns) of soft x-rays are produced from micron sized hot-spots, where plasma densities in excess of 1022 cm-3 and temperatures of ~ 1 keV are achieved. The complex physical evolution of an x-pinch is studied in detail using our three-dimensional resistive magnetohydrodynamic code (GORGON). Xray emission is preceded by the formation of jet-like structures and a miniature z-pinch plasma column (Fig. 7). A combination of radiative collapse and axial flow drive the initial radial implosion of the z-pinch until the onset of MHD instabilities further compresses regions of the plasma producing the x-ray bursts.

Figure 7: Surfaces of constant density from 3D simulation of a molybdenum xpinch.

laboratory studies of exotic highly magnetised astrophysical objects such as neutron stars.

Figure 8: X-ray image of house fly taken with Òtable-topÓ x-pinch.

Measurements of the optical and xray emission from a small 40 kA, 30 ns (10-90%) rise time X-pinch plasma discharge have also been made. Initial experiments to demonstrate the use of this X-pinch for applications in x-ray radiography have been performed (see Fig. 8). Ultra-high intensity laser interactions with solid density plasmas K. Krushelnick, A. E. Dangor, F. N. Beg, M. S. Wei, A. Gopal, M. Tatarakis One of the important characteristics of laser plasma interactions at high intensities is the efficient conversion of laser energy into relativistic electrons leading to the generation of significant return currents in the plasma. Experiments were performed using using the VULCAN laser system at RAL in which ultra-high intensity laser pulses (I > 5 x 1019 Wcm-2) were used to irradiate thin wire targets. It was observed that such interactions generate a large number of relativistic electrons which escape the target and induce multi-Mega Ampere return currents within the wire. MHD instabilities can subsequently be observed in the pinching plasma along with field emission of electrons from nearby objects.

Figure 9: High order laser harmonics ranging from 7th to 25th order (right to left). By comparing the top set (spolarised) to the bottom set (ppolarised) the magnetic field in the plasma can be determined.

Dusty Plasmas M. Coppins, M. Bacharis, J. Martin, D. Selemir Dusty plasmas are plasmas containing small solid particles. Within the last decade it has been realised that such plasmas support many unique phenomena, such as dust crystallization. However, the very basic physical processes in such systems are not very well understood theoretically. This motivates our programme of theoretical and computational studies in three main areas: dust grain charging, dust in fusion plasmas, and ÔÔmistyÕÕ plasmas. Misty plasmas are plasmas containing small liquid droplets. The charging processes are the same as for solid particles, but now surface tension plays a significant role. Using the well known Rayleigh limiting charge we find that a plasma-immersed liquid droplet will only survive if its radius exceeds a critical value given by acrit = e0fd / 4g, where fd is the potential of the droplet and g is the surface tension.

We have also made measurements of ultra-high magnetic fields produced during these interactions. We have shown that polarisation measurements of high-order VUV laser harmonics generated during the interaction (up to the 25th order) suggest the existence of magnetic field strengths of 0.7 GGauss in the overdense plasma. This technique may be useful for 27

Quantum Optics and Laser Science Head of Group: Professor J. P. Marangos The research mission of the QOLS group is to carry out basic science using lasers and to investigate, utilise and control photonic and material states and processes down to the quantum level. We include a Quantum Optics Theory team that is carrying out ground breaking research in quantum information science. Also within QOLS advanced computational techniques are being applied to research in quantum information, laser dynamics and non-linear optics and ultra-short laser pulses. There is a broad portfolio of experimental work within the group focusing on; ion trapping, atoms confined within clusters and within nanostructures, atomic and molecular coherence in nonlinear optical processes and cold matter (i.e. cold atoms, BEC's and cold molecules). Quantum Optics and Quantum Information P. L. Knight FRS, M. B. Plenio, V. Vedral, A. Beige, V. Kendon, T. Rudolph, S. Scheel. We have continued our work on all aspects of quantum entanglement. Quantum optical realisations for entanglement generation and manipulation that we have studied include Bose condensates undergoing Mott transitions while confined on an atom chip, atoms or ions trapped within high quality optical cavities and linear traps. Especially we have been interested in to what extent dissipation can be used to improve the fidelity of certain quantum computing schemes. We have achieved a full characterisation of entanglement transformations between pure states in the practically important setting of linear optical devices. We have proposed a novel protocol for the creation of long range entanglement in this setting. We have furthermore proposed protocols for the generation of entanglement between distant atoms or ions trapped 28

inside optical resonators. We have also studied the use of single photon sources in quantum communication and linear optical quantum computing. In the abstract theory of entanglement we have achieved some exciting results that suggest that entanglement manipulation can be reversible which would, if proven in general, imply a formal equivalence between such a theory of entanglement and an axiomatic foundation of thermodynamics. This work has also provided operational interpretations of hitherto entirely abstract but easily computable measures of entanglement. Our recent work has established that quantisation of the random walk, known as the quantum walk, leads to a quadratic enhancement of spreading. We have been investigating realisations of quantum walks within quantum optics, and analysing them as an example of quantum algorithms demonstrating quadratic speed-up allowed by quantum mechanics. We have investigated the effect of the field quantisation on the value of the Berry phase. We have found that there is an extra factor of one half gained by the phase even when the field is in the vacuum state (which has no classical counterpart). We suggested a feasible experiment to observe this phase in cavity-QED. We have investigated the opposite limit of the geometric phase, where there is a continuum of modes interacting with the two-level system acquiring the phase. This leads to a decohering evolution of the system and we were able to show that the phase is resistant to some errors. Our method also presents another way of defining the mixed state geometric phase that is very operational. We showed that the amount of information in a measurement involving a quantum apparatus is proportional to the amount of classical correlations between the system and the apparatus (rather than the amount of entanglement as previously thought).

http://www.imperial.ac.uk/research/qols The novel feature of our treatment has been the fact that the initial state of the apparatus has been assumed to be mixed rather than pure (as in von NeumannÕs and EverettÕs). We have also been able to derive an inequality bounding the amount of information gain by the mixedness of the initial state of the apparatus.

Figure 1: Atoms trapped in a standing light wave can be manipulated by currents provided by a chip substrate; an applied laser field from the side can modify the trapping potentials and allow tunnelling between wells to realize a quantum logic gate.

Novel Laser Phenomena and Nonlinear Atom and Photon Optics G. H. C. New, P. Kinsler, M. Yates, C. Tsangaris, J. Tyrrell Numerous theoretical projects in laser physics and nonlinear optics were undertaken. We completed an indepth study of the Virtual Source method for generating one-dimensional modes and the power method with shift that enables the Fox-Li method to be extended to the twodimensional case. We made significant progress in the modelling of transverse effects in nonlinear optical interactions. We showed that a technique based on a spatial frequency decomposition used by other authors was both cumbersome and restricted, in that it could no readily accommodate diffraction and birefringence. We developed a straightforward split-step method that was faster, and took all the main physical phenomena into account. In work on few-cycle optical pulses, we predicted the existence of a bandwidthdependent velocity shift both for c(3) (Kerr) solitons and for pairs of co-

propagating c(2) solitons. Progress was also made on the handling overlapping frequency bands in wideband nonlinear optical interactions. We started to build Finite-Difference Time-Domain (FDTD) codes for treating the nonlinear interaction of few-cycle pulses. In studying selfphase modulation, we rediscovered the problem of carrier wave shocks, and began a detailed exploration of the parameter regime in which these occurred. We initiated work on pseudo-spectral approaches to FDTD analysis which, if successful, will make the incorporation of dispersion much more straightforward. We continued work on optical parametric chirped-pulse amplification (OPCPA) and synchronously-pumped optical parametric oscillators (OPOs). We discovered a novel short-cavity operating regime in synchronouslypumped OPOs, and are currently collaborating with colleagues at St Andrews to see if the results can be reproduced experimentally. Cold Condensed Matter E. Hinds, B. Sauer, A. Curtis, S. Eriksson, B. Hall, J. Hudson, J. Rogel-Salazar, M. Tarbutt The cold matter team moved from Sussex at the beginning of 2003. Setting up the experiments in the newly renovated space in Blackett provided us the opportunity to make some significant upgrades to our apparatus. We run two experiments dedicated to studying atom optics and Bose-Einstein condensates (BEC) in miniature magnetic traps - one which relies on magnetised videotape to provide the primary trapping potential and one which uses current carrying wires. We have used the wire trap to study thermally induced spin flips in a trapped BEC. This same system was used to study the inhomogeneous magnetic field produced by the current carrying wires. The variations in the magnetic field cause the trapped BEC to fragment, an effect which needs to be understood if atom chips are to be useful for more complicated devices. Traps produced from permanent magnetic materials, like our videotape

measurements show that it should give us at least a factor of three increase in sensitivity. This would make our electron EDM experiment the most sensitive in the world. Non-linear optics in a coherently prepared molecular medium S. Gundry, M. P. Anscombe, A. M. Abdulla, S. D. Hogan, E. Sali, J. W. G. Tisch, J. P. Marangos Figure 2: 2 mm magnetic lines drawn on a Co-Pt film.

trap, do not suffer from the same inhomogeneities. We have added a tapered amplifier laser system to our videotape trap apparatus. This allows us to trap an order of magnitude more atoms and should therefore allow us to study BEC in a permanent magnet trap. We have also developed the technology to write magnetic patterns on Pt-Co multilayer films. This technique reduces the trap size by an order of magnitude compared with videotape, with a corresponding increase in trap frequency. The nanoscale traps we will be able to produce will form the cornerstone of our new programme to study BEC in low dimensions. As part of our plans to slow and trap cold molecules, we have recently succeeded in slowing a beam of YbF molecules in a alternating gradient decelerator. This work used a short electrode structure as a proof of principle. We are currently constructing a much larger decelerator which will slow YbF from 280 m/s to 80m/s, removing 90% of their kinetic energy. As part of the decelerator work we developed a pulsed supersonic source of YbF molecules. The molecules from this source form an intense, rotationally cold beam which is ideal for our experiment to measure the permanent electric dipole moment (EDM) of the electron. We have incorporated such a source into our EDM apparatus and preliminary

Figure 3: The prototype YbF decelerator.

It is well known that a gas can act as an efficient modulator for laser radiation if coherent molecular vibrations are excited within it. Sokolov et al showed in 2000 that two laser fields applied near to Raman resonance in a sample can efficiently prepare such a molecular modulator if the evolution of the system is adiabatic, thus necessitating the use of fewnanosecond laser pulses. These pulses were shown to be modulated with high efficiency in the medium to form a Òfrequency combÓ of high intensity Raman sidebands covering a remarkably broad frequency range. Due to the discrete nature of the spectrum generated by the modulator, a pulse train, rather than isolated pulses, is produced. In the case of the nanosecond fields needed to adiabatically prepare the modulator, the train of pulses produced contains about 106 members at necessarily very low energy. We have demonstrated the additional modulation of both 3 ns and 100 fs pulses in a medium in which a molecular modulator has been pre-prepared as described above. The latter case offers the possibility of the generation of a short train of about 10 high energy subfemtosecond pulses. The laser fields used to prepare the molecular modulator were at wavelengths of 807 nm and 1064 nm, coupling the fundamental vibrational transition in D2 (2993.6 cm-1). The pulse durations of these fields were 3.5 ns and 8 ns respectively, producing intensities in the range 0.4-0.8 GWcm-2. These fields were themselves modulated to produce a chain of typically 8 sidebands (see Fig. 4). This indicated that a strong molecular modulator, or coherence, had been generated in the sample. The modulation of a field at 400nm with 29

Figure 4: High order Raman sidebands of the fields preparing the molecular modulator.

a pulse duration of 3 ns was then investigated. Five sidebands were observed covering the wavelength range 294-525 nm. These sidebands were not observed if a molecular modulator was not prepared in the sample. The modulation of a second field at 400 nm, but a pulse duration of 100 fs was then investigated. We observed three Raman sidebands of the 400 nm field only when the modulator was prepared. Ion Traps and Laser Cooling R. C. Thompson, D. M. Segal The experimental work of the Ion Trap group is concerned with using laser-cooled trapped ions as a tool to perform experiments in quantum optics and fundamental physics. An ion trap is an electrode structure which holds ions at a well-defined position under ultra-high vacuum conditions for extended periods. There are two classes of trap: radiofrequency (rf) traps and Penning traps. The former employ high voltage rf potentials applied to the electrode structure to generate a three-dimensional pseudopotential well in which the ions are trapped. On the other hand Penning traps use only a static electric field and a static magnetic field to achieve trapping. We work with both types of trap but concentrate particularly on the Penning trap. We are able to load and detect a single atomic ion in our trap. The starting point for all of our experiments is to apply laser cooling to reduce the temperature of the ion or ions to within one degree of absolute zero. Ions held in a Penning trap are not as well localised as they are in an rf trap and this has, in the past, been seen as a limitation of this approach. Recently we have been investigating a technique for increasing the effectiveness of laser cooling in the Penning trap, thus improving the 30

localisation of the ion. We also have an interest in the sympathetic cooling of molecular ions, in which such ions are cooled through long-range Coulomb collisions with laser-cooled atomic ions held in the same trap.

properties.

One of the areas of strong current interest in the ion trapping community is quantum information processing (QIP). One of the greatest practical difficulties in this field is in controlling the decoherence of the delicate quantum superposition states needed. Our aim is to study decoherence processes in a Penning ion trap and develop a novel segmented miniature Penning trap for use in QIP. As part of this work we have recently achieved laser cooling of calcium ions in a Penning trap for the first time. We are also participating in new

Experiments on Rydberg atoms in crossed electric and magnetic fields have been extended into a range where manifestations of 'quantum chaos' are expected, and where theoretical predictions based on quantum mechanics presently exceed the computational capabilities of world-leading theoretical groups. Interesting regularities have been observed which extend the current state of knowledge, and the implications of our results are being assessed. Our experiment is currently the only one capable of yielding such information on systems with classically chaotic dynamics in three-dimensions.

Figure 5: A CCD image of a single axialised Mg+ ion in a Penning trap.

European Network concerned with the study of highly-charged ions in traps. Our part in this is to develop techniques for performing laser spectroscopy on such ions, which can yield important information concerning their nuclear and atomic

Confined atoms and atoms in external fields J. P. Connerade, C. Garcia-Segundo, A. J. Smith, S. D. Hogan

The theoretical study of confined atoms has been advanced through the investigation of non-spherical systems with spheroidal deformations, based on similar models for metallic clusters, and through the investigation of different types of confining shell. Our work on the development of new detectors has progressed with the support of Shimadzu Research Laboratories (Europe) Ltd, leading to a joint patent application filed on behalf of SRL and Imperial College.

Figure 7: High-lying s- Rydberg states of barium in crossed electric and magnetic fields.

Figure 6: An ion trap which may be operated as a Penning trap or as a radiofrequency trap.

Space and Atmospheric Physics Head of Group: Professor J. E. Harries The Group continues its research in three closely related areas: the physics of the Solar interior and the ionised and magnetised outer atmosphere of the Sun; the extension of the solar atmosphere into interplanetary space as the solar wind; and the physics of the EarthÕs neutral atmosphere and the role it plays in the climate system. The space programme continues to be lively and active (Fig. 1). The first of the two Double Star spacecraft was launched in late 2003 and the Rosetta spacecraft, carrying an Imperial College data processing system, was launched in March 2004. Another major mission for us is Cassini as preparations continue for the insertion of the spacecraft into Saturn orbit on 1st July 2004. We are the Principal Investigator institute for the magnetometer, and collaborators of the Ion Neutral Mass spectrometer team.

accuracy measurements have been made of the radiative energy balance of the Earth, allowing novel studies to be made of key processes within the climate system that affect the evolution of climate. Solar Physics P. Cargill, M. J. Thompson Our programme in solar physics aims at understanding the physics of the SunÕs interior and atmosphere, especially those dynamical processes that play a key role in the SunÕs 11year magnetic cycle and activity.

The first Geostationary Earth Radiation Budget (GERB-1) experiment, for which we have the Principal Investigator role, has been in operation for over a year on the European MSG-1 satellite. New, high time resolution and high

is part of a project, with the Department of Earth Sciences, to adapt geoseismic analysis techniques to studying the Sun (Fig 2). We have also continued our study of the tachocline shear region where the large-scale magnetic dynamo is widely believed to reside. Our studies of the fine structure of the solar corona have focused on the generation of synthetic emission measures differential in temperature and density, and filling factors. This permits an understanding of how the multiple temperatures and densities of the coronal plasma combine to produce the observed emission. Interpretation of coronal fine structure is a very sensitive function of the temperature used to make the observations. Heliospheric Research A. Balogh, P. J. Cargill, R. J. Forsyth, T. S. Horbury

Figure 2: High-resolution synthetic seismogram of subsurface waves travelling between different points on the sun's surface. Visible are the arrivals with (a) no intermediate bounces, (b) one bounce, (c) two bounces and (d) an asymptotic arrival.

Figure 1: Launch of the first Double Star spacecraft.

http://www.imperial.ac.uk/research/spat

We study the solar interior seismically, using observations of predominantly acoustic waves that propagate through the Sun. Our recent research has used local helioseismology to study structures and flows under sunspots and in the upper part of the SunÕs convection zone, using data from the Global Oscillation Network Group and from the MDI instrument on board the SOHO satellite. We have conducted numerical simulations to elucidate the sensitivity of tomographic data from the Sun to different aspects of the sub-photospheric structure. This

The Ulysses mission continues to provide unique observations of the heliosphere from its orbit around the poles of the Sun. After 14 successful years, the mission has been extended until March 2008. The study of Coronal Mass Ejections (CMEs) remains our main topic of interest, particularly their 3D magnetic structure as they propagate away from the Sun at all solar latitudes. Major solar outbursts unexpectedly disturbed the heliosphere in late 2003, and observations showed large CMEs dominating the heliospheric structure and dynamics. Our theoretical work has investigated the possibility of predicting the arrival time of CMEs at the Earth, and their interaction in the solar wind. We have shown that typical errors in predicting the arrival time were under 20%, despite the use of a wide range of empirical models. We have also shown that interacting CMEs undergo a form of cannibalism, with one devouring the other and are likely to be sites of enhanced production of high-energy solar cosmic rays. 31

Planetary Plasma Physics M. K. Dougherty, A. Balogh, I. Mueller-Wodarg In preparation for the arrival of the Cassini/Huygens spacecraft, we are building an empirical global magnetospheric model for Saturn to predict the magnetic field we expect to observe. We have revisited the magnetic field observations from the three previous flybys of Saturn in order to better understand both the planetÕs internal field and rotation rate. Analysis of data taken by Cassini from the Jupiter fly-by in late 2000 has continued. This data, used in conjunction with a magnetohydrodynamic model of the solar wind, has allowed us to examine the response of the Jovian magnetosphere to changes in the external driving conditions. A detailed study examined the morphology of the bow shock surface, the relationship between shock size and solar wind pressure, and waves in the upstream magnetosheath at Jupiter during the flyby. Titan has a nitrogen-rich atmosphere which extends considerably into space, compared with the moon's solid body radius. Work on a 3-dimensional global circulation model of its upper atmosphere is making predictions

Figure 4: Magnetic field and plasma data from the four Cluster spacecraft for a cusp crossing

for the observations planned for the Huygens probe and Cassini orbiter (Fig. 3). This model is also being used in science planning by the various instrument teams. Rosetta, an ESA mission to comet Churyumov-Gerasimenko, carries a data processing system provided by the group which supports the Rosetta Plasma consortium, with the aim of observing the cometÕs development from the rendezvous point in deep space in 2014 through maximum activity at perihelion. We are also a co-investigator institute for the magnetometer. Solar Terrestrial Physics A. Balogh, P. J. Cargill, C. Carr, T. S. Horbury, E. A. Lucek

Figure 3: The solar heating rates in Titan's thermosphere (ring-shaped contours) show that solar radiation poleward of around 60 deg latitude penetrates from the dayside (right) to the nightside (left). This has important implications for the global temperatures, winds and neutral and ion composition.

32

Analysis of data from the four spacecraft of the unique Cluster mission, allows us to probe the interactions between the solar wind and the EarthÕs magnetic field as well as fundamental plasma processes such as shocks and reconnection. The magnetospheric cusps, where the solar wind penetrates close to the Earth, have remained a focus of our analysis. One objective is to determine cusp structure and dynamics as a function of solar wind conditions and season. We have also shown that magnetic field turbulence in the cusps is strongly

correlated with sheared plasma flows, suggesting an origin in plasma jets associated with the magnetic reconnection process. We have also used Cluster observations to determine the sizes of structures within the EarthÕs bowshock. In some cases, shock structures are much smaller than expected from earlier data and theory, probably due to instabilities caused by energetic particle gradients and electron dynamics. Double Star is a joint project between the Chinese and European space agencies, to place two spacecraft, each carrying magnetometers supplied by the Group in Earth orbits complementary to those of the Cluster spacecraft. Analysis has started of measurements from the first spacecraft and we await the launch of the second spacecraft of this exciting mission in July 2004. Modelling of the EarthÕs Atmosphere J. D. Haigh, R. Toumi, J. E. Harries Experiments have been carried out with a simplified global circulation model to investigate the climateÕs response to solar activity. The results show a weakening and poleward shift of the sub-tropical jet streams (Fig. 5) which is qualitatively very similar to signals previously derived

Figure 5: Longitudinal average of westerly winds as a function of latitude and height. Black curve: standard atmosphere; green curve: the result of imposing heating in the lower stratosphere (only), simulating the effects of enhanced solar activity.

from observational data. This demonstrates that perturbations to the heat balance of the lower stratosphere can produce changes in the mean circulation of the lower atmosphere even without any direct forcing to the latter. Currently most numerical models that simulate cumulus and stratocumulus clouds have to use some form of temporal and/or spatial averaging of the small-scale turbulence in order to make the calculation computationally practicable. In collaboration with the Department of Aeronautics, we have developed a model that exploits a kinematic approximation of turbulence allowing us to follow individual cloud droplets. Understanding this feature is essential in determining cloudsÕ role in the dynamical-radiation feedback processes of the EarthÕs climate. We have developed a new model for storminess and droughts based on the conservation of angular momentum in a rotating frame driven by random fluctuations. This model predicts a higher return period of extreme events than standard statistical models and agrees better with observations over the UK. Earth Observation and Data Analysis J. E. Harries, J. D. Haigh, R.Toumi, V Moore We have studied the temporal variability and characteristic frequencies in the outgoing longwave radiation (OLR) emitted by the Earth, with a view to understanding the key processes that control the variability

of the EarthÕs emission to space. A comparison of observations and model results for a region of the tropical Pacific associated with El Nino shows that the model produces more power in the annual cycle than is observed, while generally reproducing the principal signatures (e.g. the El Ninos of 1982/3 and 1999). Such good simulation of observation is not repeated elsewhere around the globe and studies are continuing into the causes of this behaviour. We continue with the calibration, validation, and scientific exploitation of the GERB experiment data. The clear sky flux can only be measured in the absence of clouds, reducing the amount of available observations, but by using higher spatial resolution information from the core sensor on the MSG-1 spacecraft, SEVIRI, to look between the clouds we can estimate the clear sky flux at the GERB footprint scale. The difference between the all-sky and clear sky fluxes, is the long wave cloud forcing (Fig. 6), which provides a quantitative estimate of the reduction in the emission of radiation to space due the presence of cloud. This is a key parameter in understanding the EarthÕs radiation balance, and possible changes in this balance. Water vapour is the dominant greenhouse gas and we need to understand its variability and distribution. We found a surprising moist pool over the desert in Asia Minor during the summer in water vapour observations made from space, where one would expect a dry region of descent. We have identified a new mechanism that allows rapid turbulent pumping of water vapour into the upper atmosphere. This moisture becomes trapped in the monsoon wind fields giving rise to the observed moist pool. We are using spatial statistical analysis techniques and global data to study the energetic atmospheric response to solar particle events. Characterising the spatial and temporal scales in a global analysis will provide more insight into possible causal mechanisms.

Figure 6: Long wave cloud forcing with data presented as the 28 day mean (17/12/03-13/01/04) at the 1200 UTC time-step.

Instrumentation Development J. E. Harries, R. Toumi, J. Pickering The Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) is a unique instrument, designed to make measurements of the far infrared spectrum within the atmosphere. During flights in late 2002 over tropical Australia spectra were measured for clear skies and for cirrus cloud. Spectra were taken within the cloud where the atmosphere is opaque to TAFTS and in clear sky regions with broken cirrus above with higher transmittance regions of the spectrum show lower radiance. It is from these ÔwindowsÕ that the data will be used to probe the FIR radiance properties of cirrus ice crystals and in turn how cirrus clouds affect theradiative properties of the atmosphere. Work on further GERB instruments, to fly in a continuous operational series over the coming decade, has continued. GERB-2 and 3 have been calibrated using our Earth Observation Characterisation Facility, and GERB-4 calibration is to take place during the coming year. Our laboratory spectroscopy activities, in collaboration with Dr A P Thorne (QOLS), use our world-class high resolution visible-VUV Fourier Transform Spectrometers. We are studying atomic and molecular spectra of importance in astrophysical and planetary atmospheric physics applications, with typical accuracies of 1 part in 107 for wavelength and 10% for oscillator strength measurements. Molecular spectroscopy has involved further studies of SO2 at various temperatures. 33

Theoretical Physics Head of Group: Professor K. Stelle Our work spans a varied set of research areas with the problems of gravitation and its interactions with other matter and forces as a central theme. The Theoretical Physics Group has recently been enhanced with the arrival of Professors Chris Hull and Jerome Gauntlett and Drs Fay Dowker and Dan Waldram. With eleven current staff members, senior research fellows and long-term senior visitors such as Professors Carl Bender and Michael Green, our work is at the forefront of theoretical physics activity worldwide. Particles, Fields and Phase Transitions C. W. Bender, D. C. Brody, T. S. Evans, H. F. Jones, T. W. B. Kibble, R. J. Rivers Quantum field theory is the most successful and complete description of processes at small scales or high energies, be they fundamental particles or effective modes in laboratory materials. Current uses of field theory in the early universe and heavy-ion collisions require thermal field theory - a description of systems at high temperatures and densities which may well be out of equilibrium. As one important application, duality is being used to explain the nature of confinement in QCD-like gauge theories, which mimic the way in which the quark-gluon plasma of the hot universe condenses into hadrons. Duality is a powerful concept, whereby a quantum field theory permits totally different realisations in terms of constituent fields. We are exploring compactification techniques, whereby the three space dimensions of the real world can be replaced by a single spatial dimension for the purposes of isolating the relevant topological degrees of freedom of a 34

hot plasma. This same dual approach is enabling us to examine the analyticity of systems with high chemical potential, with direct implication for lattice calculations, for which chemical potentials pose considerable computational difficulties. In fact, one phase of QCD that may be indirectly observable in neutron stars is the colour conducting/superfluid phase of large chemical potential. A significant aspect of this is the production of vortons, vortex defects with non-trivial cores. Vorton-like defects also occur in Bose-Einstein Condensates, high-Tc superconductors and superfluid 3He. We are studying such entities in dissipative systems, to see whether they obey simple causal scaling laws in their production. Preliminary results say they do. The similarities between quantum fields in the early universe and condensed matter systems go far beyond vortons. A very fruitful approach has been to look for parallels between non-equilibrium condensed matter systems and fields in the early universe and to make predictions that can be confirmed by experiment in the former, which are impossible in the latter. To this end, we are currently performing experiments with annular Josephson junctions to test causal scaling bounds on the production of domains that mimic those of quantum field theory. After the success of our first experiment in this area, we have redesigned it to test the efficiency of causality with even greater accuracy. We have also used the results of recent experiments on the spontaneous production of magnetic flux in superconducting films to develop a better understanding of the transitions of gauge theories in the early universe. In a related context, we have used experimental results for planar liquid crystals to understand the different efficiencies in producing gross and net topological charge. Returning to gauge theories, we have used closed time-path methods

http://www.imperial.ac.uk/research/theory to show how the non-gauge environment in the early universe is the main ingredient in driving the onset of their classical behaviour. Of great importance in early universe cosmology are the details of the inflationary epoch, which is often discussed within the framework of quantum mechanics, or even in classical terms. However, a full treatment requires quantum field theory. This is a fundamentally nonperturbative problem, for which calculation techniques are sparse. To date the only available methods have been the Hartree-Fock method and the large-N expansion. In the quantum mechanical context these methods have been shown to be inferior to the linear delta expansion. This latter expansion has now been extended to continuum quantum field theory, using the closed timepath formalism, up to second order. The results are intermediate between those of the other two methods. With similar aims, lattice linear delta expansions have been performed to seventh order. In a different context, the ideas of transitions and percolation have helped us to identify many of the salient properties of networks, in their increasing use in providing descriptions of physical, economic and social systems. We have explored further the properties of systems with non-Hermitian but PT-symmetric Hamiltonians, both in quantum mechanics and in quantum field theory. In both cases we have been able to carry out a perturbative construction of an operator C, which defines a Hilbert space with a positive definite metric and so allows a probabilistic interpretation of the theory. In the area of quantum field theory we have concentrated on theories with cubic interactions. A scalar gj3 field theory is often used as a pedagogical example of perturbative renormalization even though this model is not physically realistic

(the energy is not bounded below). However, we have shown that when g = ie is imaginary, one obtains a fully acceptable quantum field theory and we have shown how to construct perturbatively the Hilbert space in which cubic scalar field theories in (D+1) -dimensional Minkowski space-time have positive spectra, are self-adjoint, and exhibit unitary time evolution. We have also studied if2c and ifcy quantum field theories. Quantum Gravity and the Foundations of Quantum Mechanics H. F. Dowker, J. J. Halliwell, C. J. Isham, I. Raptis, K. Savvidou An important approach to quantum gravity is the causal set approach, which supposes that spacetime is a discrete set with a causal order which can be thought of as a microscopic notion of before and after. We have recently proposed a model for massive particles propagating on a background causal set. The model is Lorentz invariant, in contrast to all other models of this type. It predicts that particles undergo a diffusion in momentum space and that some of them therefore will accelerate to very high energies over the lifetime of the universe providing a possible mechanism for high energy cosmic ray production. We have also worked on a model of dynamical collapse for a field theory on a lattice. Our group has continued the construction of a new approach to quantising systems whose configuration space points (or the history theory analogue) have internal structure. This is motivated by the desire to construct genuine quantum theories of causal sets, or space or space-time topologies: systems that cannot be handled using standard quantisation methods that assume the configuration/history space to be a differentiable manifold. The central idea in this scheme is to identify the entities of interest as objects in a category, whose arrows then play a role analogous to that of momentum in standard theories. This new scheme reproduces the

standard techniques for manifolds, but includes very many systems that cannot be handled at all by conventional methods. In view of the grave failure of classical differential geometric methods in attempts to quantise general relativity by retaining a smooth background geometrical spacetime manifold, our work has opted for an alternative combinatory-algebraic route to quantum gravity. In the past year, we have continued a major project of applying MalliosÕ recently developed Calculus and, in extenso, base manifold-free, sheaf-theoretic Abstract Differential Geometry to a finitisticalgebraic scenario for quantum spacetime structure and dynamics that was proposed by us in connection with SorkinÕs causal set approach to Lorentzian quantum gravity. In another development, we have continued a detailed study of the problem of continuous time in the consistent histories programme. In particular, the main contribution here has been the development of the temporal structure of the histories formalism based on the key observation that ÒtimeÕÕ arises in the theory in two natural waysÑ-as the label in temporal logic, and as the label in dynamics. The most recent result of this work came from the study of a histories version of general relativity, which combines the Lagrangian and Hamiltonian formalism. It allows the coexistence of covariant objects, such as the Lorentzian four-metric, with canonical ones, such as the spatial three-metric, in a way that preserves their geometric relations. This property guarantees the spacetime character of the canonical variables. A number of our recent papers have concerned the application of the decoherent histories approach to models that do not possess a time coordinate, such as one encounters in quantum cosmology. We have also worked on a very general understanding of the emergence of classical physics from quantum theory, and in particular, understanding how effective evolution equations of hydrodynamic form can arise. We have recently

given a specific demonstration of this in the context of oscillator chain models. We have also been investigating how entanglement is destroyed by a decohering environment in some simple models. String Theory and M-Theory M. Abou-Zeid, A. Fotopoulos, J. P. Gauntlett, M. B. Green, P. Henri-LabordŽre, C. M. Hull, J. Kalkkinen, M. Majumdar, D.Martelli, P. Pouliot, J. Sparks, K. S. Stelle, A. A. Tseytlin, D. Waldram One focus of our work has been AdS/CFT duality, which relates string theories in curved backgrounds to gauge theories. Building on our successful semiclassical approach to quantisation of superstrings in AdS5 ´ S5 in the large R-charge sector (small strings with large angular momentum), we have developed a more general perspective on the possible string states that should be dual to ÒlongÕÕ gaugeinvariant operators with several large spins. One can compare their energy as a function of the spin to anomalous dimensions of the corresponding operators. This led to a remarkable new test of the AdS/CFT duality for non-supersymmetric states and a new perspective on their classification. The rotating string solutions are described by a special integrable system - the Neumann model of an oscillator on a sphere. Integrability on the string side appears to be related to integrability of the spin chain model, the Hamiltonian of which represents the (one-loop) anomalous dimension operator in gauge theory. Supersymmetric backgrounds play central roles as M-theory vacua or solitons and also as the gravity duals of supersymmetric field theories in the AdS/CFT correspondence. Without matter these backgrounds are special holonomy manifolds, and recent work has focussed on a generalisation to the case with nform flux. A central idea is the use of G -structure and intrinsic torsion to characterise the geometry. This has 35

led to a complete classification of the supersymmetric solutions of various supergravity theories, and the structure conditions typically have a simple interpretation in terms of generalised calibrations. This approach has led to the explicit construction of a number of interesting new solutions. A particularly important application is to find new gravity duals to supersymmetric field theories. We have found the form of the most general warped M-theory backgrounds with an AdS3, AdS5 or flat Minkowski factor, and several new classes of solution were found. In certain cases these are dual to type IIB backgrounds and provide new examples of SasakiÑEinstein metrics. The dual field theories can also have the interesting property of a non-compact R-symmetry. This approach has led to a novel and general construction of SasakiÑ Einstein metrics of any dimension as bundles over KŠhlerÑEinstein spaces. Key to these examples is whether the n-form fluxes are suitably quantised. In this context we have also given a proof of the FreedÑWitten anomaly shift in the flux quantisation on a D6-brane, relating it to the corresponding shift in four-form quantisation in M-theory. We have also followed an alternative approach to the study of supersymmetric solutions through generalised holonomy. This led to interesting differences between the classical and quantum theories, giving important clues to the symmetry structure of quantum M-theory. We have also studied the string-theory corrections to spaces of special holonomy, particularly the first non-trivial corrections which are quartic in curvatures. These generate soft deformations of KŠhler and G2 holonomy manifolds that nonetheless preserve the corresponding Killing spinor structures. This analysis also yields explicit expressions for the corrections to non-compact CalabiYau and G2 manifolds of interest for braneworld cosmological models. We have studied strings in curved 36

gravitational plane-wave backgrounds, with potential applications to cosmological singularity issues. For a large class of time-dependent plane-wave backgrounds, first-quantised string theory can be solved exactly in terms of free oscillators and its spectrum can be studied explicitly. In the case of singular backgrounds, one is able to specify certain boundary conditions under which string propagation is not sensitive to the singularity at the origin. Similar work was done in the context of ÒstandardÕÕ cosmological backgrounds, suggesting that string resolution of singularities happens in a more general context. We have studied the implications of the superalgebra structure of supersymmetric plane wave backgrounds. We have found an extension of the usual KŠhler type of supersymmetric sigma model to complex flat geometry. We have investigated the geometry of gauge fields on Mbranes, in particular the associated holonomies and their cohomological structure. We have analysed certain random walks (Stochastic Loewner Evolution) on Riemann surfaces using conformal field theory. We have analysed brane dynamics and tachyon condensation. We showed that small dimensional branes have the highest survival probability in a gas of different dimensional branes and antibranes. We have also constructed an unusual inflationary scheme generated by tachyons in a certain large N limit. Cosmology and Varying Constant Theories M. Blasone, T. W. B. Kibble, J. Magueijo, M. Majumdar, L. Pogosian We have played a leading role in the quest for methods for testing the hypothesis that the spectrum of cosmic microwave bacground (CMB) fluctuations is Gaussian. With the release of the first-year WMAP data, our group has provided a large number of data analysis tools for this. This work made use of advanced computing facilities supplied by the COSMOS supercomputing consortium. We have also established an

important connection between nonGaussianity and the possibility of non-trivial cosmic topology. We suggested that CMB fluctuations might have a thermal origin, and investigated the CMB power spectrum in scenarios with defects and inflation, and under quintessence. The group was also instrumental in establishing a framework for relating the theory and observations of a varying fine-structure constant. This ranged from dilatonic to varying speed of light (VSL) theories; our work has spurred an extensive continuing litterature on both astronomical and laboratory implications of this subject. A highlight of our recent research was the discovery that varying constant theories may play an important role in the quantisation of gravity. Our work on the non-linear realisations of the Lorentz group, and on deformed dispersion relations, has triggered much subsequent work on methods for implementing invariant quanta of space and time. It was shown that such VSL quantum gravity theories may explain the presence of ultra high energy cosmic rays, opening up the door to observational quantum gravity. In this context, we found that the bosonic string, subject to appropriate dispersion relations, does not need to have a tachyonic ground state. The black hole metric may run with energy leading to a very different spectrum for high temperature Hawking radiation, and with a concomitant different endpoint for black-hole evaporation.

Undergraduate Teaching Director of Undergraduate Studies: Professor R. C. Thompson Senior Tutor: Dr R. J. Forsyth Admissions Tutor: Professor W. G. Jones The Blackett Laboratory, the largest Physics Department in the UK, welcomes about two hundred new undergraduate students each year. We offer three year and four year undergraduate degree programmes designed to match the pre-university experience of students from the UK, Europe and overseas. These degree programmes lead to either the BSc or the MSci degrees of the University of London (under special regulations for Imperial College). The Degree Programmes There are six degree programmes, and the course structure allows easy transfer between most of the programmes in the early years. Three Year Programmes BSc

Physics

BSc

Physics with Theoretical Physics

Four Year Programmes BSc

Physics with Studies in Musical Performance

MSci

Physics

MSci

Physics with a Year in Europe

MSci

Physics with Theoretical Physics

The Department also offers a four year BSc in Physics with a Year in Europe, but students are not normally admitted to this programme in Year 1. The Department aims to provide all students on all degree programmes with courses of the highest quality, giving them the opportunity to develop

http://www.imperial.ac.uk/physics/courses/ug

their knowledge and understanding of Physics to a level which equals or exceeds that offered by any other university in the UK. We have recently completed a major review of our programmes to ensure that they are up-to-date and meet changing expectations regarding international (particularly European) standards. The Departmental Staff/Student committee is very active and makes an important contribution to the design of the curriculum and to improvement in teaching. All programmes start with a firm foundation in core physics and mathematics followed by a broad and flexible range of options in the later years. In the first three years, students receive tutorials in groups of four from academics and other researchers. Courses are lectured by experts in the field, and the breadth and depth of research activity in this large department enables us to give students knowledge of the frontiers of research in a wide range of specialities in physics. The department was one of only three in the whole country to receive the top grade of 6* in the 2003 Research Assessment Exercise. It also has a teaching quality assessment of ÔexcellentÕ. The lecturers are drawn from our nine internationally recognised research groups: ¥ Astrophysics ¥ Condensed Matter Theory ¥ Experimental Solid State ¥ High Energy Physics ¥ Photonics ¥ Plasma Physics ¥ Quantum Optics and Laser Science ¥ Space and Atmospheric Physics ¥ Theoretical Physics. We also draw on expertise in other departments to offer Mathematics and Biophysics courses. Final year projects are offered in all these research areas, providing an opportunity for students to work alongside

academic staff, research fellows, research assistants and postgraduate research students. MSci or BSc ? Broadly speaking, students aiming for a career as a professional physicist or wishing to understand physics at the frontiers of research should follow the MSci programme both for the additional content and also for the opportunity to develop professional skills and undertake a major project. The MSci is the normal route to a PhD. The BSc is aimed at a wide variety of students who wish to follow careers outside specialised research. Many employers value the numeracy and problem-solving skills of physicists. For example, many physics graduates find their degree an excellent platform for a career in finance. Some students choose the three year BSc as a rapid and less extended route into careers based on physics in industry and public service. Others aim for a research career in physics by taking the BSc followed by a specialist MSc. The First Year Courses in the first year cover:¥ Electricity & Magnetism ¥ Electronics ¥ Mechanics ¥ Quantum Physics ¥ Relativity ¥ Structure of Matter ¥ Vibrations & Waves ¥ Professional Skills I ¥ Mathematics I ¥ Mathematical Analysis ¥ Physics Laboratory I ¥ Physics Short Experiments and Project I Weekly seminar groups in the first year include group projects, development of problem solving skills, and exploration of research articles, web sites and research data. For most students, the first year 37

practical class consists of sessions on optics, electronics and computing of four weeks each. In the First and Second Years we teach computer programming in C++, a valuable skill which is attractive to future employers. Students then choose between Mathematical Analysis and more laboratory work. For those choosing laboratory, four weeks are spent on short experiments designed to complement the first year physics lectures. The majority of students then carry out a six week project working in small groups supervised by active researchers. The projects culminate in two open days on which staff, other students and sixthformers view poster presentations on the projects. The Second Year Second year core courses cover:¥ Electromagnetism ¥ Electrons in Solids ¥ Optics ¥ Quantum Mechanics I ¥ Applications of Quantum Mechanics ¥ Statistical Physics ¥ Statistics of Measurement ¥ Thermodynamics ¥ Mathematics II ¥ Professional Skills II ¥ Physics Laboratory II BSc and MSci Physics students choose a Level 2 option from:¥ ¥ ¥ ¥

Sun, Stars & Planets Physics Applied to Medicine Mathematical Methods Language

Second year laboratory work includes experiments on Spectroscopy, Diffraction & Holography, Interferometry, Waves & Propagation, Radioactivity, Solid State Physics, Operational Amplifiers and Computing. Emphasis is placed on the development of a range of experimental techniques as well as more general professional skills such as writing reports, keeping a laboratory note book, and assessment of experimental errors.

38

The Third Year All BSc and MSci Physics students take core courses in:¥ Nuclear & Particle Physics ¥ Solid State Physics ¥ Atomic & Molecular Physics ¥ Professional Skills III ¥ Physics Laboratory III

MSci Fourth Year

BSc candidates have to complete a project, which may be laboratory based or theoretical. MSci and BSc candidates take the Comprehensive Papers (see below), and complete their third year with a selection of Level 3 options. The more theoretical physics lecture courses are marked with a (T) ¥ Advanced Classical Physics ¥ Astrophysics ¥ Dynamical Systems & Chaos ¥ Foundations of Quantum Mechanics ¥ Group Theory ¥ Instrumentation ¥ Lasers, Optics & Holography ¥ Molecular Biophysics ¥ Plasma Physics ¥ Statistical Mechanics

¥ Philosophy ¥ Politics ¥ The Roman empire ¥ Science, culture & display

(T) (T) (T)

(T)

Students on Physics with Theoretical Physics courses replace Laboratory III with an extra theoretical option. All students may choose up to one Level 2 option (see above) and up to one Level 4 option (see below). They may also include one of the following courses provided by the Humanities Programme and Business School:¥ Accounting ¥ Art & nature ¥ Communicating science: The public & the media ¥ Controversies & ethical dilemmas in science & technology ¥ Creative writing ¥ European history (1870-1989) ¥ History of medicine ¥ History of science ¥ History of technology ¥ Language ¥ Macro-economic policy ¥ Modern literature & drama ¥ Music & western civilisation

In their fourth year MSci students complete a major project with a research group. This gives students an opportunity to get to grips with an extended project that lasts the whole year and relates to current research activities. In some cases, the project results in the publication of a research paper. Under the guidance of a lecturer, students learn how to set goals and plan their work to achieve them. Reading begins at the end of Year 3 for a literature survey to be presented at the start of Year 4. Thereafter students learn to design an experiment, formulate new experimental results or develop computer software, and to present their results in oral and written presentations. The project is coupled to the Research Interfaces course which develops professional skills. This course explores the subjects of project management, written communication, financial management and spoken communication, culminating in a group business proposal. Another aim is to give students a working knowledge of the vocabularies relating to research in universities, business and industry. MSci students choose a selection of Level 4 options, and may study one Level 3 option (see above). The Level 4 options are ¥ Atmospheric Physics ¥ Biophysics of Nerve Cells & Networks ¥ Computational Physics (T) ¥ Cosmology ¥ Device Physics ¥ General Relativity ¥ Laser Technology ¥ Optical Communications ¥ Particle Physics (T) ¥ Quantum Coherence in Solids (T) ¥ Quantum Field Theory (T) ¥ Quantum Optics ¥ Space Physics ¥ Unification (T)

MSci Physics with Theoretical Physics Students who choose to follow this four year MSci programme concentrate on the more theoretical options. In their first year they take an extra formal Mathematical Analysis course instead of project work and in their second year the Mathematical Methods option. In Year 3 these students take Advanced Classical Physics instead of laboratory. The fourth year project is theoretical and students take a specified number of theoretical options.

Year in Europe Host Institutions IDEA League

UN KIN ITED GDO M

ESPC I

Students carry out a research project in a research group. They are assessed on their written project report, a report from their supervisor, and an oral presentation in the host language. In addition to the research project, students attend physics lecture courses and sit examinations, written or oral, in the host language. As preparation for their year abroad they take language courses in both their first and second years and are recommended to take Mathematical Methods in their second year. In their fourth year, MSci Year in Europe students sit the Comprehensive Papers, take Nuclear and Particle Physics, Solid State Physics and Nuclear & Particle Physics, together with a range of options drawn from the

tand e

r

S P A I N

Orsay

Karlsru

he

Erlangen Freiburg Lausan S W I T Z E R ne ZurichL A N D Grenob le Trento Padova ITAL Y

FRA

San

Students are visited twice during their year abroad by a member of staff who normally is very familiar with the host country and university.

Hamburg

GERM ANY Aachen

The Year in Europe Programme The MSci in Physics with a Year in Europe is of four years duration, the third year being spent at a host university in continental Europe. Year in Europe students have derived great benefit and enjoyment from this opportunity to widen their experience. They usually go to Europe on ERASMUS/SOCRATES exchange programmes.

Delft

NCE

Vale ncia

La L a (Ten guna erife )

third and fourth year programmes including the Research Interfaces course. The research project completed abroad counts as their MSci project. We have established links with host universities in France, Switzerland, Germany, Italy and Spain. These are: UniversitŽ de Paris XI (Orsay), Ecole SupŽrieure de Physique et de Chimie Industrielles (Paris), Institut National Polytechnique de Grenoble, Ecole Polytechnique FŽdŽrale de Lausanne, UniversitŠt ErlangenNŸrnberg, UniversitŠt Freiburg, UniversitŠt Hamburg, UniversitŠt Heidelberg, Universitˆ degli studi di Padova, Universitˆ degli studi di Trento, Universitat de Valencia, Universidad de La Laguna (Instituto de Astrof’sica de Canarias), and Universidad de Cantabria (Santander). Each of these universities has high standing and extensive research activity. Some have exceptional facilities in particular research fields.

For example, La Laguna is excellent for Astrophysics because of the siting of many astronomical telescopes in the Canary Islands. Imperial also has formal links with the IDEA League Universities of Delft, Aachen and ETH Zurich. Physics with Studies in Musical Performance The musical life of Imperial College has always been strong and many physics students have demonstrated high ability in musical performance. The joint degree programme with the nearby Royal College of Music is for physics students who can also reach the RCMÕs stringent admission standards in musical performance. This programme provides students with a high quality honours BSc qualification in physics while providing musical training to the highest international standards. The music component consists mainly in high level performance tuition by the Professors of the Royal College of Music but also includes stylistic and historical studies. The Imperial 39

College Director of Music is actively involved with this course. Students on this programme have given public recitals, performed as concerto soloists, and won national competitions such as the BBC Radio 2 Young Musician of the Year.

over recent years and in 2002 was over 26%, which significantly exceeds the national average for physics. This increase has been helped by the College's ÔtasterÕ courses called WISE (Women into Science and Engineering) which we operate in July each year.

The Comprehensive Papers Our degree programmes contain a most valuable and unique component: the two comprehensive examination papers. These carefully constructed papers are designed to test our studentsÕ ability to apply the core physics taught in earlier years of the course to new situations. To do well, students need to gain an overview of the whole of physics, and to see links and similarities between different areas. Students are prepared for these examinations through special tutorials to develop these analytical and problem solving skills, which are so important for a practising physicist. Most candidates complete these papers in their third year. Undergraduate Admissions Applications for our undergraduate courses are received through the UCAS system from all parts of the world although most are from the UK. We wish to encourage applications from all sectors, particularly from areas traditionally under-represented in higher education and from other European countries. We are looking for students of high ability and motivation with the potential to do well on our courses. Offers of places are conditional on achieving high grades in physics and mathematics at A-level and in a third subject. The average of the grades of students admitted is significantly above AAB (for the best 3 A-levels). We also admit students offering the International and European Baccalaureate, French Baccalaureate, German Abitur, US Advanced Placement examinations and school leaving qualifications from many other countries. The percentage of women undergraduates admitted onto our programmes has steadily increased 40

Our students have wide interests and abilities, particularly in music, the arts and sports, as well as being among the most talented in the land in physics. They go on to a wide variety of careers after graduation and a recent European wide survey has indicated that their rating of both the employment potential of their degree and of the quality of their university experience are much higher than the European average. All applications receive careful attention and those applicants that appear to be well suited to our courses are invited for a visit and interview. These visits take place in small groups between early November and early March and consist of a tour of the campus, usually including a Hall of Residence, guided by an undergraduate, followed by a meeting with the Admissions Tutor or one of his colleagues on the admissions team. This is designed to give applicants information about the courses and the facilities and also about life in Imperial College and London. There is then a tour around the department followed by a short individual interview. The latter helps us to get to know the student as an individual and is mainly concerned with interests and motivation. It also enables applicants to raise questions of particular interest to them. Our high international profile is manifested in many ways, not least through our membership of several strategic alliances with major universities in Europe (e.g. CLUSTER and the IDEA League). In addition about thirty students from universities throughout Europe and further afield come each year to study in the Department for selected final year courses and laboratory work. Most come under ERASMUS/SOCRATES

exchange student programmes. These Occasional Students, and those European and International students enrolled on our three and four year degree programmes, greatly enhance the rich cultural and national diversity of the Department. Schools Liaison School liaison is a high priority within the Department, and we offer visits to schools and Òguided toursÓ. We also offer places to a number of school students undertaking work experience training. We have extended our reach geographically: for example, Physics has been featured in the annual Imperial College recruitment visit to Hong Kong. The Department, in association with the College and the University of London, has an extensive range of out-reach programmes. These are free and are designed to introduce physics to potential undergraduates. The most popular is the Open Day, focussed around a display by First Year students of their project work, and held around the third week of June. There are also various Masterclasses held at various times during the year. The highly popular two-day Women in Science and Engineering courses, held in June/July, are specifically designed to encourage women students to consider a degree course in one of the science or engineering disciplines.

Postgraduate Studies Director of Postgraduate Studies: Dr Julia Sedgbeer The Physics Department is one of the most prestigious postgraduate schools in Physics in the UK. In terms of research it uniquely covers the most comprehensive range of important experimental and theoretical research fields. These extend from astronomy, space and plasma physics to high energy, theoretical and atomic physics. Solid state, laser physics, applied optics and photonics have wide applications, while fields such as quantum information theory may lead to exciting new applications. There are close links with the biophysics research group (part of the Department of Biological Sciences), which is also housed in the Blackett Laboratory. There are many examples of international and industrial collaboration involving our nine research groups. There are also interdisciplinary centres where researchers from different groups or from different Departments collaborate closely to benefit from each otherÕs expertise. The Department has extensive facilities and a tremendous range of research topics available to postgraduate research students.

http://www.imperial.ac.uk/physics/research/pg/

degree in Physics or a related subject. The usual length of registration for a PhD degree is three years. In addition to research training, the Department offers postgraduate taught courses leading to the MSc degree of the University of London and the DIC. The Department offers two MSc courses: Optics and Photonics and Quantum Fields & Fundamental Forces. Further details of these MSc courses are given below. The Graduate School of Engineering and Physical Sciences (www.imperial.ac.uk/gradeps/) has been established to develop and enhance the academic experience of graduate students at the College. It provides training programmes and workshops in professional and other skills, undertakes quality assurance of graduate programmes, organises events, such as guest lectures and symposia, and promotes career opportunities for graduate students. Very few institutions world-wide are able to offer such a

wide range of opportunities in postgraduate physics. Further information can be found in the Postgraduate Study in Physics booklet, at www.imperial.ac.uk/publications/pgb/ General information about graduate studies at Imperial College London can be seen at www.imperial.ac.uk/pgoptions. MSc in Optics and Photonics The MSc course in Optics and Photonics has been running in its present form since October 2001 and draws on the skills of staff actively involved in optics research. The title reflects the fact that the course covers both the traditional areas of optics, which are of key importance to the application of optical techniques, and the important areas of photonics, notably optical communications and laser physics. The course aims to provide the professional skills in optics that are in demand by industry and academia.

Information about the research being undertaken in the particular groups and centres can be found under their sections elsewhere in this report; further details can be obtained from the individual Heads of Group (see page 53). The Department provides facilities and supervision for students to engage in research work leading to a higher degree of the University of London (MPhil or PhD), and to the Diploma of the Imperial College (DIC). About 60 postgraduate research students join the Blackett Laboratory each year, the majority being UK students with about 25% from other EU countries and about 15% from overseas. The normal qualification for acceptance for research training is a first or second class honours 41

There are a large number of employment opportunities in optics and photonics throughout the UK and the rest of Europe, not only in optical communications but also in many other areas of applied photonics. The main components of the 12-month MSc Optics and Photonics course are lectures, laboratory experiments and a fourÐmonth project. In the first term, there are four Foundation lecture courses in Information and Telecommunications, Imaging, Lasers, and Optical Measurement and Devices. In addition, there are sessions dedicated to the development of professional skills. There are occasional seminars on the application of optics technology in industry, together with seminars on research and development in universities and industry. In the second term, a number of option courses are offered, including Optical Fibres, Optical Communications, Optical Design, Optical Design Laboratory, Optical Fibre Sensors, Laser Optics, Laser Technology, and Optical Displays. The laboratory experiments cover a wide range of subjects and are spread over approximately 54 halfdays in the first and second term, teaching key laboratory skills and techniques. The project lasts from mid-May to mid-September, and many projects can be carried out in industry. Examples of recent projects are · A new method of producing unidirectionality in solid-state ring lasers · Polymer/nanocrystal blends for solar cells, · Femtosecond pulse shaper using a spatial light modulator, · Adaptive optics for the human eye, · MEMS based digital filter, · Optical modelling and optimisation of organic LED structures, and · Fluorescence lifetime imaging applied to microscopy. There are a significant number of EPSRC funded places for suitably qualified UK students. Funding is 42

also available to cover the fees for suitably qualified students from other EU countries. MSc in Quantum Fields and Fundamental Forces The Theoretical Physics Group runs this very successful MSc course, attracting around 15 students annually. It is normally a one-year course but can also be taken part-time over two years. A series of lecture courses occupies the year up to May and students spend the summer on a project leading to the writing of a dissertation. The course is intended to bridge the gap between undergraduate-level work and the research frontier in theoretical physics. Many successful students have gone on to do a PhD either at Imperial College London or at another major university. Unfortunately, no financial support is available for students attending the course. The lecture courses currently being offered are: Compulsory lecture courses: Quantum electrodynamics Unification Advanced Quantum Field Theory

Optional courses: Supersymmetry Cosmology and Particle Physics Topics in Classical and Quantum Gravity String Theory Differential Geometry Special Topics (short specialist courses on topics of current interest) Available undergraduate courses: Foundations of Quantum Theory Group Theory Dynamical Systems and Chaos General Relativity Courses are offered subject to staff availability; certain courses may not be offered in a given academic year. Students are assessed by examinations and a project dissertation. The examinations are on the compulsory courses and on four optional courses, which may include up to two undergraduate options. Examinations on all the courses are held in May. There are also informal tests on the compulsory courses in January. MSc students are also encouraged to attend the regular weekly seminars at which visiting speakers present recent research results, as well as internal seminars by research students. These are supplemented by an interCollegiate programme of weekly seminars on string theory and related subjects.

PhD Degrees awarded in the Department in 2003 Astrophysics

R. S. Ferguson ÒCharacterisation of Silicon-Germanium Heterostructures by Kelvin Force MicroscopyÓ Supervisors: Prof. B Joyce & Dr K Fobelets (Electrical Engineering)

L. Clewley ÒDetermine the Mass of the Milky Way Using Blue Horizontal Branch StarsÓ Supervisor: Dr S J Warren

D. G. Gevaux ÒSpectroscopic Study of Mid-Infrared Light Emitting DiodesÓ Supervisor: Prof. C. C. Phillips

J. V. Dawson ÒZeplin III: A TwoPhase Xenon WIMP DetectorÓ Supervisor: Prof. T J Sumner

J. W. Gray ÒResonant Cavity Light Emitting DiodesÓ Supervisor: Prof. G Parry

D. C. R. Davidge ÒDevelopment of a Two Phase Xenon Detector for use in Direct Dark Matter SearchesÓ Supervisor: Prof T J Sumner

A. D. Hartell ÒSurface Segregation of As During the Epitaxal Growth of SiÓ Supervisor: Dr J Zhang

L. E. Harley ÒObservation and Outflow Modelling of Luminous Cataclysmic Variable StarsÓ Supervisor: Prof. J. E. Drew

H. M. Liem ÒRaman Spectroscopy on Conjugated Polymers-Effective Probe of Molecular Orientation and Phase Transitions in Conjugated PolymersÓ Supervisors: Prof. D D C Bradley & Dr P Etchegoin

K. Kolokoutsas ÒMCW 297, A Case Study of a Massive Young Stellar ObjectÓ Supervisor: Prof. J E Drew S. K. Mattila ÒSupernovae as Probes of their Host Galaxies and Circumstellar Environments: Search Strategies in Nuclear Starbursts and Spectroscopy of the SN 1987A CSMÓ Supervisor: Prof. W P S Meikle Experimental Solid State Physics A. J. Bennett ÒA Study of InGaAs/ GaAs Quantum Dots and GaInNAs/ GaAs Quantum Wells for Optoelectronic Applications at 1300 nmÓ Supervisors: Prof G Parry & Dr R Murray

S. Malik ÒTuning of Optical Properties of INAS/GAAS Self-Assembled Quantum DotsÓ Supervisor: Dr R Murray C. L. Olson ÒCharge Accumulation and Recombination in NanoCrystalline Metal Oxide ElectrodesÓ Supervisor: Dr J Nelson R. Pacios ÒOrganic Photovoltaic Cells and Photodiodes Based on Conjugated PolymersÓ Supervisor: Prof. D D C Bradley D. Poplavskyy ÒHole Injection and Transport in Organic SemiconductorsÓ Supervisor: Dr J Nelson High Energy Physics

A. J. B. Borak ÒOptical Studies of Thermal and Electronic Properties of Quantum Cascade LasersÓ Supervisor: Prof. C C Phillips D. B. B. Bushnell ÒOptimisation of Strain-Compensated Multi-Quantum Well Solar CellsÓ Supervisor: Prof. K W J Barnham & Dr J Zhang D. T. D. Childs ÒProperties and Device Applications of 1.3mm emitting InAs/GaAs self Assembled Quantum DotsÓ Supervisor: Dr R Murray

E. P. Corrin ÒDevelopment of Digital Readout Electronics for the CMS TrackerÓ Supervisor: Prof. G Hall J. R. M. S. Goncalo ÒMeasurement of the high-Q2 Neutral Current Deep Inelastic Scattering Cross Sections with the ZEUS detector At HERAÓ Supervisor: Dr K R Long R. D. Hill ÒA Measurement of Rb at LEP2 with the ALEPH DetectorÓ Supervisors: Dr J K Sedgbeer & Prof. D M Websdale

P. N. Martin ÒMeasurements of Atmospheric Trace Gasses Using Open Path Differential UV Absorption Spectroscopy for Urban Pollution MonitoringÓ Supervisors: Dr J F Hassard & Dr R Toumi E. A. Noah Messomo ÒRadiation and Temperature Effects on the APV25 Readout Chip for the CMS TrackerÓ Supervisor: Prof. G Hall M. Petteni ÒThe Jet Response and the Search for the Higgs Boson in the Channel ZH ->e+e- bbbar with the Df DetectorÓ Supervisor: Dr G J Davies S. A. Rutherford ÒColour Reconnection Studies at LEP2 with the ALEPH detector and Data Reduction Algorithms for the CMS Electro-Magnetic CalorimeterÓ Supervisor: Dr C Seez B. M. C. Simmons ÒRing Imaging Cherenkov Counters for LHCbÓ Supervisor: Prof. D M Websdale Optics - Photonics L. Bollini ÒCharacterisation of Semiconductor Optical Amplifiers Through Bias Current ModulationÓ Supervisor: Dr M W McCall P-A. Champert ÒHigh Power Master Oscillator Powerful Fibre Amplifiers for Frequency ConversionÓ Supervisor: Prof J R Taylor C. W. Dunsby ÒWide-Field CoherenceGated Imaging Techniques Including Photorefractive HolographyÓ Supervisor: Prof. P M W French D. S. Elson ÒDevelopment of Ultrafast Laser Technology and its Application to Fluorescence Lifetime ImagingÓ Supervisor: Prof. P M W French S. E. D. Webb ÒDevelopment and Application of Widefield Fluorescence Lifetime ImagingÓ Supervisors: Prof P M W French & Dr M J Lever (BAMS) 43

Optics - Quantum Optics and Laser Science M. P. Anscombe ÒNonlinear Optics with Atomic CoherenceÓ Supervisor: Prof. J P Marangos R. J. Blackwell-Whitehead ÒHigh Resolution Fourier Transform Spectrometry of the Spectrum of Neutral ManganeseÓ Supervisors: Prof P L Knight & Dr J C Pickering I. Fuentes Guridi ÒEntanglement and Geometric Phases in LightMatter InteractionsÓ Supervisors: Dr V Vedral & Prof. P L Knight J. L. K. Koo ÒLaser Cooling and Trapping of CA+ Ions in a Penning TrapÓ Supervisors: Prof. R C Thompson & Dr D Segal H. F. Powell ÒQuantum Optics With A Single Trapped IonÓ Supervisors: Prof. R C Thompson & Dr D M Segal J. Rogel-Salazar ÒAspects of BoseEisntein Condensation and Bessel Beam ResonatorsÓ Supervisor: Prof. G H C New J. Sudbery ÒStudies of Laser Cooled Calcium Ions in the Penning and Combined TrapsÓ Supervisors: Dr D M Segal & Prof. R C Thompson D. R. Symes ÒHigh Intensity Laser Interactions with Extended Atomic Cluster and Microdroplet MediaÓ Supervisor: Dr R A Smith B. K. Tregenna ÒManipulation of Quantum Information in Decoherent EnvironmentsÓ Supervisor: Prof P L Knight

Plasma Physics J-W Ahn ÒInvestigations of the Boundary Plasma in the MAST TokamakÓ Supervisor: Dr M Coppins A. Ciardi ÒModelling of Hypersonic Jets in Wire Array Z-Pinch ExperimentsÓ Supervisor: Dr J P Chittenden H. M. Davies ÒThe role of finite larmor radius (FLR) in instability in the compressional Z-pinchÓ Supervisor: Prof M G Haines

J. I. S. Syroka ÒOn the Withdrawal of the Indian Summer MonsoonÓ Supervisor: Dr R Toumi N. S. Trasi ÒA Finite ElementSpherical Harmonics Model Applied to Radiative Transfer in Inhomogeneous CloudsÓ Supervisors: Prof J D Haigh & Dr C De Oliveira (Royal School of Mines) Theoretical Physics

P. B. Jones ÒAn Experimental Investigation into Tokamak edge MHD BehaviourÓ Supervisor: Dr M Coppins J. G. Ruiz Camacho ÒPlasma Dynamics of two-wire z pinchesÓ Supervisor: Prof. M G Haines

R. E. Clark ÒVacua and interpolating solutions in supergravityÓ Supervisor: Prof. K S Stelle J. D. Fearns ÒFoundations of Quantum Physics in Smooth ToposesÓ Supervisor: Prof. J C Isham

Space and Atmospheric Physics J. M. Gloag ÒResearch into Weak Interplanetary Shock Waves using the Ulysses SpacecraftÓ Supervisor: Prof. A Balogh A. L. Hadley ÒNon-Linearities between Atmospheric Sulphur and Sulphur EmissionsÓ Supervisor: Dr R Toumi G. Matthews ÒSensitivity of a Geostationary Satellite Radiometer to Scene and Detector NonUniformitiesÓ Supervisor: Prof. J E Harries M. J. Owens ÒThe Role of Coronal Mass Ejections in Space WeatherÓ Supervisor: Prof. P J Cargill A. C. Pagel ÒAnalysis of Turbulent Intermittency in the Heliospheric Magnetic Field using Ulysses dataÓ Supervisor: Prof. A. Balogh. G. Pettinato ÒInvestigation of Atmospheric Trends and PeriodicitiesÓ Supervisor: Prof. J E Harries

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A. Rees ÒUlysses Observations of Magnetic Clouds in the 3-D HeliosphereÓ Supervisor: Dr R J Forsyth

M. Ivin ÒTopics in Quantum Field TheoryÓ Supervisor: Dr T S Evans E. Kavoussanaki ÒTopological Defects in the Universe and in Condensed Matter SystemsÓ Supervisor: Dr R J Rivers

Research Grants The following grants, valued at over £16.3 million, were initiated during 2003. Imperial College Trust P M W French Nervous system mediated hypersensitivity states fluorescence microscopy £2,663,267.00 Royal Society D J Waldram Royal Society Fellowship £196,305.26 Royal Society I C F Mueller-Wodarg Royal Society Fellowship. £202,756.69 Royal Society C M Hull The Structure of M-Theory and String Theory Dualities (Royal Society Wolfson Research Merit Award). £225,000.00 Royal Society M J Damzen Adaptive Gain Interferometer £68,704.00 Leverhulme Trade Charities Trust D D C Bradley Triplets states in polymer light-emitting displays £36,098.00

Commission of European Communities E A Hinds Quantum Gates and Elementary Scalable Processors Using Deterministically Addressed Atoms (QGATES) £73,305.00 Commission of European Communities E A Hinds Preparations and applications of quantum-degenerate cold Atomic/ molecular gases £85,788.00 European Commission K W J Barnham A New PV Wave Making More Efficient Use of the Solar Spectrum (FULLSPECTRUM) £376,000.00 Matsushita Electric Works Ltd J Nelson Organic solar cell durability research £114,450.00 Qineti Q T J Sumner Energetic particle shielding and interactions software tool £27,200.00 BP International Limited D D C Bradley Organic Electroluminescent Lighting £209,994.00

Royal Society E A Hinds Royal Society USA Research Fellowship (Dr Elizabeth Anne Curtis ) £36,000.00

Molecular Vision Limited D D C Bradley A low cost point-ofcare test kit for microalbuminuria £147,786.00

Leverhulme Trade Charities Trust M B Plenio Royal Society/Leverhulme trust senior research fellowships £32,239.00

Shimadzu J-P Connerade Detecting Mirror project £85,000.00

Commission of European Communities M B Plenio Quantum Properties of Distributed Systems - Thematic Network. £18,000.00 Commission of European Communities V Vedral Topological quantum information processing £101,281.00 Commission of European Communities D M Segal Quantum Gates and Elementary Scalable Processors Using Deterministically Addressed Atoms (QGATES) £1,560,000.00

National Physical Laboratory R C Thompson Cold trapped Ions for Quantum information processing £52,320.00 AWE Plc R W Smith Plasma Physics Lectureship £300,815.00 NPL Management Limited L Cohen NPL student sponsorship agreement £18,000.00 Particle Physics and Astronomy Research Council T J Sumner Development on Inertial Sensor Charge Management System for SMART2 (and LISA). £90,869.00

Particle Physics and Astronomy Research Council J C Pickering Astrophysical Laboratory Spectroscopy: Improving the atomic data for astrophysics by high resoultion Fourier Transform Spectroscopy £110,996.00 Particle Physics and Astronomy Research Council J E Drew Towards an understanding of accretion on to Herbig and T Tauri stars £184,635.00 Particle Physics and Astronomy Research Council C Paterson High Angular Resolution Imaging £165,452.00 Particle Physics and Astronomy Research Council A Balogh Post Launch operations support for the Rosetta Plasma Consortium instruments at Imperial College £241,262.00 Particle Physics and Astronomy Research Council J E Kalkkinen M-Theory solutions and geometry (PPARC Fellowship) £120,394.00 Particle Physics and Astronomy Research Council D I Britton GRIDPP Project Manager Costs £82,012.00 Particle Physics and Astronomy Research Council C Paterson A complete toolkit for adaptive optics. £341,658.00 Engineering & Physical Science Research Council P Tšršk Polarisation coding in high density optical data storage £89,378.00 Engineering & Physical Science Research Council E A Hinds The UK cold atoms: Network UKCAN £49,625.00 Engineering & Physical Science Research Council G Parry Quantum Light Emitting Diode for Secure Comms. £256,761.00

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Engineering & Physical Science Research Council L Cohen Novel Growth and Optimisation of the Magnetic Properties of Sr2FeMo06 Thin Films. £263,655.00 Particle Physics and Astronomy Research Council S C Cowley Magnetic field generation in astrophysical plasmas £52,947.00 Engineering & Physical Science Research Council J W G Tisch Basic Technologies: Attosecond Technology - Light Sources, Metrology and Applications. £1,012,726.00 Engineering & Physical Science Research Council P L Knight Decoherence in Quantum Information Processing. £208,058.00 Engineering & Physical Science Research Council A J Campbell Reactive, Polymerisable Organic Light Emitting Diodes (RPOLED). £299,587.00 Particle Physics and Astronomy Research Council A Balogh Participation in the Magnetic Field Investigation on the Venus Express Mission. £107,562.00 Particle Physics and Astronomy Research Council M K Dougherty Magnetometer Investigation for Cassini Saturn Orbiter. £998,776.32 Engineering & Physical Science Research Council A J Campbell Electrical And Optional Studies of Conjugated Semiconducting Polymers And Their Devices. £123,255.00 Particle Physics and Astronomy Research Council K Long Research and development on cooling of intense muon beams and experimental demonstration of muon ionisation cooling £23,018.00 Engineering & Physical Science Research Council P Tšršk 100 Fold increase of optical 46

data storage capacity using singular beams and multiplexing £104,541.00 Particle Physics and Astronomy Research Council G Hall The CMS Experiment at the Large Hadron Collider - Completion of the Detector and the Road to Physics £118,336.00 Engineering & Physical Science Research Council L Cohen Raman spectroscopy and ellipsometry of potential spintronic (half metallic) Ferromagnetic materials £21,100.00 Natural Environment Research Council H E Brindley Aerosols in the Earth's climate: studies of the spectral properties, variability, and climatic effects based on new satellite observations £139,570.60 Engineering & Physical Science Research Council R J Rivers Complex Extension of Quantum Field Theory. £92,025.00 Particle Physics and Astronomy Research Council E A Lucek Physics of Boundaries and Waves in Collisionless Plasmas £226,725.00 Particle Physics and Astronomy Research Council M Petteni Higgs Searches at the Tevatron with D0: Including Methods to Improve the Search Sensitivity £100,548.00

Engineering & Physical Science Research Council M W McCall Complex Electromagnetic Media - Beyond Linear Isotropis Dielectrics £13,633.00 Engineering & Physical Science Research Council J B Pendry Metamaterials create new horizons in electromagnetism £154,793.00 Engineering & Physical Science Research Council T G Rudolph Local and extendedparty quantum information processing £203,593.00 Engineering & Physical Science Research Council J B Pendry Metamaterials create new horizons in electromagnetism £459,832.00 Engineering & Physical Science Research Council V Vvedensky Self-assembled low dimensional semiconductor nanostructures £129,131.00 Particle Physics and Astronomy Research Council E A Hinds Centre for the measurement of Particle Electric Dipole Moments: Imperial College site £65,851.00 Engineering & Physical Science Research Council E A Hinds Deceleration of cold molecules £66,550.00

Particle Physics and Astronomy Research Council P J Dornan TIER-2 Technical Coordinator £26,898.00

Engineering & Physical Science Research Council J F Sparks M-Theory and exceptional holonomy £37,671.00

Particle Physics and Astronomy Research Council T J Sumner Galactic Dark Matter Search at Boulby: Years 2003 to 2007 £1,123,834.00

Stanford University T J Sumner Flight charge management for drs on smart2 £111,956.00

Particle Physics and Astronomy Research Council K S Stelle M-Theory, Cosmology and Quantum Field Theory £748,893.00 Engineering & Physical Science Research Council J R Taylor All-fibre ultrashot pulse sources £360,448.00

Sandia National Laboratories R W Smith Readership in experimental Z-pinch based high energy density physics £409,566.00 University Of Cambridge L Cohen Enhanced Critical Currents and Pinning in Superconducting MgB2 by Chemical Modification £107,335.00

Collaborations Physics is an international science, and many aspects of our research involve collaborations with colleagues at institutions in the UK and throughout the world. These include: Air Products and Chemicals Inc., USA Anglo Australian Observatory, Australia Arhus University, Denmark Astrophysics Research Institute British Petroleum International, UK California Institute of Technology, USA Centre dÕEtudes des Rayonnements Spatiaux (CERS), France CERN CNR-IFAC, Firenze, Italy Complutense University, Madrid Cornell University, USA Delft University of Technology, The Netherlands Donostia International Physics Center (DIPC), San Sebastian, Spain Ecole Polytechnique Federale Lausanne (EPFL), France Eidgenossische Technische Hochschule (ETH), Switzerland EI Du Pont de Nemours and Company, USA Endoscan Ltd ESA-ESTEC, Holland European Southern Observatory Free University of Amsterdam, The Netherlands Free University Berlin, Germany Free University of Brussels, Belgium Ghent University, Belgium GKSS, Germany Goddard Space Flight Center, USA Graz University, Austria Hadley Climate Research Centre Harvard Smithsonian Center for Astrophysics, USA Harvard University, USA Herriot Watt University Hewlett-Packard Laboratories, USA High Altitude Observatory, USA HRL Laboratories LLC, Malibu, USA INAOE, Mexico

Institute for High Energy Physics, Russia Institute for Space Research, Austria Institute for Nuclear Physics, Bulgaria Institute of Chemical Physics, Spain Institute of Nuclear Research, Russia International Space Science Institute, Switzerland Isaac Newton Group, La Palma, Spain Jet Propulsion Laboratory, USA Kentech Instruments Ltd KFKI, Budapest, Hungary Kings College London Los Alamos National Laboratory, USA Lucent Laboratories Massachusetts Institute of Technology, USA Matsushita Electric Works, Japan Max Planck Institute, Garching, Germany Max Planck Institute, Heidelberg, Germany Max Planck Institute, KattenburgLindeau, Germany MEMC Electronic Materials Inc., USA Merck Ltd, UK NASA Langley Research Center, USA National Institute Standards and Technology, USA National Physical Laboratory National Solar Observatory, USA NRL Washington, USA Observatoire de Nice, France Padua Observatory, Italy Pennsylvania State University, USA Perimeter Institute, Waterloo, Canada Philips Research, The Netherlands Pilsen University, Czech Republic Research Center of Crete, Greece Royal Meteorological Institute, Brussels, Belgium Rutherford Appleton Laboratory Sandia National Laboratory, USA Scottish Environment and Energy Foundation Space Telescope Science Institute Stanford University, USA Steacie Institute for Molecular Sciences, Canada

Stockholm Observatory, Sweden Technical University of Braunschweig, Germany Technical University of Denmark, Lyngby, Denmark Technical University of Vienna, Austria Technion, Israel THALES Paris, France The AtlantIC Alliance The Dow Chemical Company, USA Trieste Observatory, Italy UK Meteorological Office UMIST Universidad Aut—noma de Madrid, Spain Universidad de Zaragoza, Spain UniversitŽ Louis Pasteur, Strasbourg, France University University University University University

College London of Arizona, USA of Athens, Greece of Austin, USA of Bangor

University of Barcelona, Spain University of Basilicata, Italy University of Birmingham University of Bologna, Italy University of Bonn, Germany University of Braunschweig, Germany University of Bristol University of Buenos Aires, Brazil University of California Los Angeles, USA University of California San Diego, USA University of Cambridge University of Chemnitz, Germany University of Cologne, Germany University of Colorado, USA University of Hampton, USA University of Hertfordshire University of Hawaii, USA University of Kaiserslautern, Germany University of Leeds University of Leicester University of Naples, Italy University of Neuchatel, Switzerland 47

University of Newcastle University of New South Wales, Australia University of Nottingham University of Oslo, Norway University of Otago, New Zealand University of Oxford University of Paris XI, Orsay, France University of Palermo, Italy University of Potsdam, Germany University of Reading University of Rochester, USA University of Salerno, Italy University of Sheffield University of Siena, Italy University of Southampton University of St Andrews University of Strathclyde University of Surrey University of Sussex University of Sydney, Australia University of Texas at Austin, USA University of Valencia, Spain University of Wales, Aberystwyth University of Warwick University of Wurzburg, Germany University of York Washington University, St. Louis, USA Weizmann Institute, Israel Wellesley College, USA We are members of a significant number of European Union and other collaborative programmes, including: ACQUIRE, a European Union training network AEOLOS, the assessment of the impact of SF6 and PFC reservoir tracers on global warming ALEPH experiment, CERN ASTRO-F consortium Australian Network of Excellence on Atom Interferometry Basic Technology Attosecond Programme British Petroleum International (UK) Ð Imperial College Engineering for Sustainable Development Programme CMS collaboration

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COCOMO, a Research Training Network on coherent control of atomic processes Consortium for Computational Quantum Many-Body Theory COSLAB, an ESF Programme on Cosmology in the Laboratory D0 Consortium, Fermilab, USA ELAIS survey EPSRC Experimental and Theoretical Studies of Electrical Transport in Organic Electroluminescent Devices Programme EPSRC Polymer Blend Semiconductors Programme EPSRC Retinomorphic Imaging Basic Technology Programme ESF Network on Quantum Information processing ESF-QIT programme on Quantum Information Theory and quantum computation European Union training network on Cold Quantum Gases FASTNET, a European Union training network Framework VI, Nanotechnology; British Council/DAAD ARC programme FERRUM project: oscillator strengths for astrophysics applications HERSCHEL SPIRE consortium HITRAP, An Ion Trap Facility for Experiments with Highly-Charged Ions HYTEC, a CEC Framework V IHP Network IR studies of nearby type II supernovae ISCOM, a EU Network on the Information Society as a Complex Network ISD LINK (DTI/EPSRC) Late-time spectroscopy of type Ia supernovae London Centre for Nanotechnology NANOFAB, a European Union training network PLANCK HFI consortium POE, a European Community RTN POWERPLAY, a CEC CSG programme project Ultrafast Photonics Collaboration (UPC IRC) Ultrafast spectroscopy of conjugated polymers SLAM, a programme on Future and Emerging Technologies SWIRE, the NASA SIRTF Legacy Survey

QUEST, a European Union IHP Network collaboration on Quantum Optics QGATES, a European Union IST Network collaboration on quantum gates for quantum computing QUBITS, an IST Network on decoherence in atomic logic elements QuICT, a UK EPSRC Network collaboration on quantum information and coherence QUIPROCONE, a European Union IST Network of Excellence coordinating body on quantum information processing throughout Europe QUPRODIS, a Thematic Network on the Quantum Properties of Distributed quantum systems Search for supernovae in starburst galaxies SOLICE, Solar influences on Climate and the Environment Spin Polarised Magnetics Oxides network and Spintronics Network Studies of SN 1987A at very late phases SupIRCam, A tool for understanding the IR light curves of type Ia Supernovae The host galaxies of high redshift type Ia supernovae The Physics of Type Ia Supernova Explosions The progenitors of massive, corecollapse supernovae UKCAN, the UK cold atoms network UK GridPP Project UKIRT Infrared Deep Sky Survey UK Mid-Infrared network UK National Carbon Based Electronics Consortium

Technical Development, Intellectual Property and Commercial Interactions Many aspects of the research in the department have the potential for commercial opportunities. Much of our work requires the development of technologies to facilitate fundamental scientific projects yet there is a growing recognition that a number of these technologies merit protection through patenting. The Department has a wide range of commercial interactions. We collaborate with companies as partners in large European projects, DTI Link projects, Basic Technology, etc. Ph.D students within the Department benefit from direct sponsorship by industry and EPSRC CASE awards. Companies support our research directly and provide Ôin kindÕ support (such as loan of equipment, access to facilities). We also have a good track record of licensing our intellectual property and working with industry as consultants. In addition, the Department currently has 5 successful spin out companies. Our technology development and commercial activities include the following: Astrophysics The experimental part of Astrophysics is dedicated to the development of 0.1-100 keV particle detectors and associated technology (high precision ultra high vacuum technology in copper, gas purification, charge/light readout technologies, position reconstruction, cryogenics) for the dark matter project and charge control systems and associated technology (UV light sources, particle guns, satellite instrumentation) for the gravitational wave project. The Group collaborates with QinetiQ, Carlo Gavazzi Space (Italy) and the Jet Propulsion laboratory (USA). Condensed Matter Theory The Group has a wide-ranging research portfolio with a strategic focus on materials for electronic and photonic devices, and has developed theoretical and computational expertise in the modelling of these materials. Many projects have direct relevance to the next generation of technologies. These include the development of

new materials for the "perfect lens" in near-field optics, plasmonic and photonic structures, nano-electromechanical devices, and the growth of thin films and quantum dots. Techniques include quantum Monte Carlo simulations, kinetic Monte Carlo simulations and density functional theory. The Group has a close working relationship with BAE, Astron and Antenova and holds several patents. Experimental Solid State Physics The group develops technologies across a very broad range of areas. Molecular electronic materials provide a novel class of semiconductor with applications in flat panel electroluminescent displays and lighting, TFT arrays and memory devices, imaging devices and solar cells, optical amplifiers

and lasers, and microanalysis systems for chemical and biological detection. Air Products and Chemicals Inc, British Petroleum, BP Solar, Du Pont, Matsushita Electric Works, Merck and Molecular Vision have directly funded research in the group during 2002-2003. In addition, we have had collaborative projects with Cambridge Display Technology and Philips (CEC POWERPLAY), Covion GmbH, and The Dow Chemical Company. Consultancy has been undertaken for both industrial corporations and venture capital organisations.

Finally, the group also has several patents in this technology area and a spin out company, Molecular Vision Ltd, has been set up. Inorganic opto-electronic emitters, detects and modulators are being developed for use in the data and telecomms areas. The work is collaborative with Toshiba, Sharp, Zarlink, Bookham, TTP and IQE. Design and growth of single photon sources and long wavelength detectors is another active area using InAs quantum dot technology for quantum cryptography and telecomms applications. The work is collaborative with Toshiba and Bookham. In collaboration with QinetiQ, Bell Labs, and Thompson CSF, quantum cascade lasers are being developed for optical communications. We hold 3 patents in these areas. Optical Products have funded CASE studentships in novel inorganic photovoltaics, an area where we hold three patents. BP Solar fund our work into novel inorganic photovoltaics and thin film silicon cells. As part of the EU Framework VI integrated project ÒFull SpectrumÓ we are collaborating with Nanoco and Solaronix. NPL currently sponsor Ph.D students in Spintronics and in optical spectroscopy for single molecular detection. NECI support our work in high mobility narrow gap semiconductors for hybrid sensor technology. In the areas of superconductivity and magnetism we collaborate with QinetiQ, NPL and Oxford Instruments. High Energy Physics The Group has a long tradition of technology transfer, with an emphasis in advanced instrumentation and detector technologies, optoelectronics and biomedical applications but with interests in the financial, energy and general instrumentation sectors. Group members have filed about 28 patents in support of their technology Ð more than CERN. Early work by David Binnie, Julia Sedgbeer and Ray Beuselinck led to a novel suite of software for gamma 49

camera production, which is now adopted world-wide by a number of industrial groups. The Group develops technology in a range of areas. Gamma-cameras, radiation hard electronic, silicon sensors, digital read out and control electronics, fibre-optic links and plastic explosive detection (using diamond detectors and fast neutron sources). The Group has developed a generic approach to ultra-high throughput genomics, proteomics, and health care diagnostics for DNA sequencing, protein mapping and ultrafast protein folding. This technology has been adopted by a number of biotech and pharmaceutical companies and is being developed into a generic discovery platform with a wide range of applications in drug discovery and development, diagnostics, general molecular biology in genomics and proteomics, and biological threat assessment and mitigation. The Group has a growing influence in Grid technologies, where there is a convergence between high throughput systems for biomedical applications and those pioneered for Tevatron and LHC areas. The EPSRC funded ÔDiscovery NetÕ (with Hassard co-PI, in collaboration with the Department of Computing (DoC)) seeks to apply HEP approaches to processing vast quantities of data to a range of industrial applications where the bandwidth, multiple source and visualisation issues are closely related (such as bio-informatics). John Hassard has worked with Geoff Rochester of Astrophysics in a novel renewable energy system Ð tidal stream power. This uses several tools common to approaches common in particle physics, most notably finite element analysis. Several municipalities (most notably the City and

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Photonics Direct support for our research into high-resolution imaging comes from Glaxo-SmithKline and Kentech Instruments. Scientific Generics plc, Kodak Ltd, Kentech Instruments Ltd and ICR/ Royal Marsen NHS Trust have all supported CASE awards. ÔIn kindÕ support has come from Optical Insights, Inc, LaVision Biotec GmbH, PicoQuant GmbH and Kentech Instruments Ltd.

County of San Francisco) have adopted this technology, together with some major UK and non-UK utilities. The Group has spun out a number of companies (deltaDOT Ltd, Diamond Optical Technologies Ltd, HydroVenturi Ltd among others), which have raised finance and are progressing their commercial relationship with other companies, and with a large number of UK, US and other companies in several sectors. Laser Consortium Our technology is associated with developing high intensity and ultra short laser pulses. Theoretical descriptions of the effect of these intense fields have led to technology that can be used to produce microscopic optical structures by laser induced modification (through multiphoton ionisation) of media. The attosecond basic technology programme promises to open up new fields of ultra high time resolution measurement in surface science etc. Plasmas produced by interaction of short pulse lasers with sub wavelength clusters are a promising source for x-ray generation at lithographically important wavelengths. They also produce high energy density plasmas of interest for testing of numerical codes. We currently have an on going collaboration including funding from AWE in this area.

The Group, in the area of high power lasers and nonlinear optics, holds one patent on optical amplifying devices. Pilkington Optronics (now Thales) have supported CASE awards and Ôin kindÕ support has come from Shell Research Labs, SpectraPhysics and Spectron Laser Systems. The fibre laser programme includes development of MOPFA (Master Oscillator Power Fibre Amplifier) technology including development of versatile compact seed sources, which are deployed together with high power, fibre-based amplifiers (Yb, Yb-Er and Raman) to generate high average power sources with versatile wavelength and pulse formats. The fibre work has longstanding collaboration and support from the IPG Group of Companies The Group has one spin out company Holoscan UK Ltd funded through the University Challenge Seed Fund. Plasma Physics The Group is engaged in research involving the technology of high voltage pulsed power and high power lasers. We also work in the development of Òtable-topÓ sources of x-rays, neutrons and particle beams for technological applications. In addition, we have a research programme into the development of ion thrusters for spacecraft propulsion and satellite positioning. We have collaborations with a number of external companies and organisations which provide CASE awards and other support. These include UKAEA Culham, AWE Aldermaston plc., QintetiQ, Titan Pulsed Sciences Corp., Sandia

National Laboratory, Kentech Instruments Ltd, the Laboratory for Laser Energetics (University of Rochester), the Institute for Laser Engineering (University of Osaka) and the Lawrence Livermore National Laboratory. Quantum Optics and Laser Science The Group applies cutting edge laser technology to a broad range of measurement and control problems in basic physics research. The Centre for Cold Matter has an ongoing collaboration with the K. J. Lesker company investigating transparent conductive films for polymers. Dr D. M. Segal and Prof. R. C. Thompson have ongoing collaborations with the National Physical Laboratory (NPL) on ion trapping and the development of ultra-stable lasers. This includes supervision of students funded by the NPL who carry out most of their experimental work there, but who are registered as students at Imperial College.

Space and Atmospheric Physics The Group develops magnetometers, light weight cryogenic systems, far infra-red detector arrays, multiinstrument digital electronics and spectrometer designs for space missions. It also develops high resolution UV and VUV Fourier transform spectroscopy particularly detector arrays and beam splitters. The Group collaborates with Ultra Electronics and SIRA as well as the MET office and the USA and French Navy. Theoretical Physics The dominant part of the GroupÕs activities lies in constructing theories of the fundamental nature of the universe (M-theory, quantum cosmology, brane-cosmology, astroparticle physics, etc.). None of these require the development of any technologies. However, subsidiary activities of the Group may lead to novel applications of superconducting devices (through the ESF Cosmology in the Laboratory (COSLAB) programme), or have implications for the modeling of

commercial and industrial activity (through the EU The Information Society as a Complex System (ISCOM) network) or for the modelling of commercial products (e.g. financial derivatives). An example of such subsidiary activity is the work of Dr M. Blasone to develop and patent the "MetaPassword" system for secure access to a communications network, based on biometric data. He, and his partners at the University of Salerno, developed a business plan for commercialisation of this system and it was entered in the UK Research Councils Business Plan Competition. It was one of only two such projects from Imperial to be accepted into the final round of competition. Students in the Group have developed various database algorithms and have formed a company to exploit these ideas.

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Academic Staff Professors Space Physics A Balogh, DIC, MSc Physics K W J Barnham, PhD Physics A R Bell, MA, PhD Experimental Solid State Physics D Bradley, BSc, PhD, ARCS, FRSA, CPhys, FRS Physics P J Cargill, BSc, PhD Atomic and Molecular Physics J-P Connerade, PhD, ARCS, DIC Plasma Physics S C Cowley, BA, MA, PhD Applied Optics J C Dainty, PhD Experimental Particle Physics P J Dornan, BA, PhD, FRS Physics J E Drew, BSc, PhD Physics P M W French, PhD Physics J P Gauntlett BSc, PhD Atmospheric Physics J D Haigh, DPhil Physics G Hall, BSc, PhD Theoretical Physics J J Halliwell, BSc, PhD Earth Observation J E Harries, BSc, PhD Quantum Optics E Hinds, BA, DPhil, FRS Physics C M Hull, BA, PhD, FlnstP Laser Physics M H R Hutchinson, PhD Theoretical Physics C J Isham, PhD, ARCS Physics W G Jones, PhD, ARCS Quantum Optics P L Knight, DPhil, FRS Theoretical Solid State Physics K M Krushelnick BSc, MA, PhD Physics A Mackinnon, PhD Laser Physics J Marangos, PhD Physics W P S Meikle, PhD, FRAS Nonlinear Optics G H C New, DPhil Applied Physics G Parry, BSc, PhD, DIC Theoretical Solid State Physics Sir J B Pendry, MA, PhD, FRS Experimental Solid State Physics C C Phillips, PhD Physics M B Plenio, Dr. rer. nat Astrophysics M J Rowan-Robinson, PhD Physics R W Smith, MA, PhD, DIC

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(as of 31st December 2003) Physics D J Southwood, BA, PhD, DIC Theoretical Physics K S Stelle, PhD Experimental Astrophysics T J Sumner, DPhil Ultrafast Physics and Technology J R Taylor, BSc, PhD Physics M J Thompson, BA, MA, PhD Physics R C Thompson, MA, DPhil Physics A Tseytlin, MS, PhD Physics T S Virdee, PhD Theoretical Solid State Physics D D Vvedensky, PhD Physics D M Websdale, PhD, ARCS

Senior Research Fellows Dr. T C Bacon, BSc, PhD Emeritus Prof. D M Binnie, PhD Emeritus Prof. D D Burgess, MA, PhD, DIC Emeritus Prof. I Butterworth, PhD, CBE, FRS Prof. A D Caplin, MA, MSc, PhD Emeritus Mr. A E Dangor, BSc Prof. M G Haines, PhD, ARCS, FRCO, ARCM Dr. H F Jones, BA, PhD Emeritus Prof. B A Joyce, DSc, FRS Prof. T W B Kibble, MA, PhD, FRS Prof. E Leader, BSc, MS, PhD Prof. L B Lucy, BSc, PhD Prof. R Newman, PhD, FRS Prof. J J Quenby, BSc, PhD, DIC, ARCS Dr. A P Thorne, MA, DPhil

Readers Physics L F Cohen, BSc, PhD Physics M J Damzen, PhD High Energy Physics P D Dauncey, BA, DPhil Space Physics M K Dougherty, BSc, PhD High Energy Physics C Foudas, MA, M.Phil, PhD Physics W M C Foulkes, PhD Physics J F Hassard, PhD Physics S Lebedev, MS, PhD Physics K R Long, BSc, DPhil Theoretical Physics J C R Magueijo, BA, PhD Photonics Physics M W McCall, PhD Physics J Nash, PhD Physics J Nelson BA, PhD Physics R J Rivers, PhD Laser Physics R A Smith, BSc, PhD

Atmospheric Physics R Toumi, PhD, ARCS Physics V Vedral, BA, PhD Physics S J Warren, BA, PhD

Senior Lecturers D I Britton, BSc, MSc, PhD R G Burns, PhD J P Chittenden,PhD, DIC, BSc, CPhys, MInstP K Christensen, PhD M Coppins, PhD H F Dowker BA, MA, PhD T S Evans, BA, PhD R J Forsyth, BSc, PhD R Murray, BSc, PhD, K Nandra, BA, PhD J K Sedgbeer, PhD, DIC D M Segal, BSc, DPhil K Weir BSc, PhD J Zhang, BSc, ARCS, PhD, DIC

Advanced Fellows A Beige, BSc, PhD H. E. Brindley, BSc, PhD D C Brody, BSc, MSc, PhD R S Garcia A Goussiou, BS, PhD T S Horbury, BSc, PhD A H Jaffe, MSc, PhD R Jesik, BSc, MSc, PhD E A Lucek, BSc, PhD I C F Mueller Wodarg, MSc, PhD C Paterson, BA, PhD M Petteni, PhD S V Popov, MSc, PhD T G Rudolph, BSc, PhD D J Waldram. BA, MA, PhD

Lecturers A J Campbell, BSc, MSc, PhD G J Davies, BSc, PhD U Egede, BSc, PhD C N Guy, PhD R J Kingham, BSc, PhD D K K Lee, BA, PhD I Liubarsky, BSc, PhD, CPhys, MinstP, FRAS V Moore, PhD Z Najmudin, BA, PhD M A A Neil, BA, PhD J C Pickering, BA, MA, PhD, DIC B Sauer, BA, PhD J W G Tisch, BSc, PhD P Tšršk, DPhil, PhD Y C Unruh, MSc, PhD

Visiting Professors M E Barnett, BSc, BA, PhD D Cotter, BSc, PhD, DSc R G Evans, BSc, PhD, FlnstP J Gallop, BA, DPhil P Gill, BSc, DPhil I Grant, FRS R Hastie, BSc, MSc Sir M J Rees, MA, PhD FRS A D Sokal, AB, AM, PhD J C Thompson, MA, PhD

Contacts Astrophysics Group Head of Group: Professor M Rowan-Robinson Tel: 020 7594 7530, Fax: 020 7594 7541, e-mail: [email protected]

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Condensed Matter Theory Group Head of Group: Professor D D Vvedensky Tel: 020 7594 7605, Fax: 020 7594 7604, e-mail: [email protected]

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Experimental Solid State Physics Group and Centre for Electronic Materials and Devices Head of Group: Professor K Barnham Tel: 020 7594 7565, Fax: 020 7581 3817, email: [email protected]

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High Energy Physics Group Head of Group: Professor P J Dornan Tel: 020 7594 7822, Fax: 020 7823 8830, email: [email protected]

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The Laser Consortium Director: Professor J P Marangos Tel: 020 7594 7857 Fax: 020 7594 7714, email: [email protected]

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Photonics Head of Group: Professor P M W French Tel: 020 7594 7706, Fax: 020 7594 7714, email: [email protected]

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Plasma Physics Group Head of Group: Professor K Krushelnick Tel: 020 7594 7635, Fax: 020 7594 7658, email: [email protected]

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Quantum Optics and Laser Science Head of Group: Professor J P Marangos Tel: 020 7594 7857 Fax: 020 7594 7714, email: [email protected]

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Space and Atmospheric Physics Group Head of Group: Professor J E Harries Tel: 020 7594 7670, Fax: 020 7594 7900, e-mail: [email protected]

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Theoretical Physics Group Head of Group: Professor K Stelle Tel: 020 7594 7826, Fax: 020 7594 7844, e-mail: [email protected]

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