The Nobel Prize in Physics 2011 was awarded to the puzzling discovery that the Universe is not only expanding, but doing so with ever increasing speed, whereas in the standard picture of cosmology it was expected to slow down. This acceleration could either be due to a new exotic matter component called dark energy which is repellent and would form the major ingredient of the cosmos. Alternatively, the laws of gravity as predicted by Einstein's general relativity may not be quite correct on cosmological scales and need to be modified. One of the best ways to pin down the properties of dark energy and test general relativity on cosmological scales is to study the large-scale distribution of matter in the Universe and its evolution, together with its gravitational interactions. In a novel approach to probe this distribution, I am going to simultaneously analyse the positions, the velocities, and the shapes of millions of distant galaxies. The clustering of galaxies in space provides a picture of the underlying matter distribution since galaxies trace the matter density. However, the picture is biased because galaxies preferentially reside in high-density regions, and this galaxy bias limits the cosmological information that can be extracted from clustering. Using galaxy velocity measurements, one can infer the coherent motions of galaxies due to the large-scale gravitational forces via so-called redshift-space distortions, causing apparent overdensities of galaxies when these are attracted by a large mass. This effect needs to be disentangled from the actual clustering of galaxies, which is again hindered by galaxy bias, so that the power of redshift-space distortions alone to constrain cosmological parameters is limited as well. General relativity predicts that large masses can deflect light rays similar to a magnifying glass - therefore the term gravitational lensing was coined for this effect. The images of distant galaxies are distorted by the gravitational lensing of the large-scale structure of the Universe between these galaxies and Earth. These 'cosmic shear' distortions directly map the intervening matter distribution, without any dependence on galaxy bias. In addition, cosmic shear also probes the geometry of the cosmos as it depends on the distances between the light sources, the lenses, and the observer. This potentially very powerful cosmological probe is plagued by intrinsic alignments of galaxy shapes which mimic the distortions characteristic of cosmic shear and hence limit the accuracy of cosmological measurements. The key to overcome the limitations of the three probes is to analyse them jointly and also include their cross-correlations into the analysis. This will lift degeneracies between parameters as for instance caused by the galaxy bias, and calibrate systematic effects such as the intrinsic alignment contamination of cosmic shear. With this technique I will obtain significantly better constraints on dark energy and the laws of gravity than from any individual probe, and the results will additionally be much less susceptible to systematic errors. This approach requires an imaging survey with excellent image quality to measure the shapes of faint and small galaxy images which overlaps with a redshift survey that allows for the accurate measurement of galaxy distances which are needed to measure clustering and redshift-space distortions. The research team that I am going to lead has access to a unique pair of such surveys. The quality and size of the joint data set is so good that I can target different types of galaxies at the same time and thus apply even more advanced techniques to eliminate systematic effects from the measurements. The joint scientific analysis will therefore yield unprecedented precision and accuracy on the properties of dark energy and the nature of gravity.

Light is a versatile tool for imaging and engineering on microscopic scales. Optical microscopes use focused light so that we can view specimens with high resolution. These microscopes are widely used in the life sciences to permit the visualisation of cellular structures and sub-cellular processes. However, the resolution of an optical microscope is often adversely affected by the very presence of the specimen it images. Variations in the optical properties of the specimen introduce optical distortions, known as aberrations, that compromise image quality. This is a particular problem when imaging deep into thick specimens such as skin or brain tissue. Ultimately, the aberrations restrict the amount of the specimen that can be observed by the microscope, the depth often being limited to a few cellular layers near the surface. This is a serious limitation if one wants to observe cells and their processes in their natural environment, rather than on a microscope slide. I am developing microscopes that will remove the problematic aberrations and enable high resolution imaging deep in specimens.Focused light also has other less well-known uses. It can be used to initiate chemical reactions that create polymer or metal building blocks for fabrication on the sub-micrometre scale. These blocks, with sizes as small as a few tens of nanometers, can be built into structures in a block-by-block fashion. Alternatively, larger blocks of material can be sculpted into shape using the high intensities of focused lasers. These optical methods of fabrication show potential for use in the manufacture of nanotechnological devices. When manufacturing such devices, the laser must be focused through parts of the pre-fabricated structure. The greater the overall size and complexity of the structures, the more the effects of aberrations degrade the precision of the fabrication system. My research centres on the use of advanced techniques to measure and correct such distortions, restoring the accuracy of these optical systems.Traditional optical systems consist mainly of static elements, e.g. lenses for focusing, mirrors for reflecting and scanning, and prisms for separating different wavelengths. However, in the systems I use the aberrations are changing constantly. Therefore they require an adaptive method of correction in which the aberrations are dynamically compensated. These adaptive optics techniques were originally developed for astronomical and military purposes, for stabilising and de-blurring telescope images of stars and satellites. Such images are affected by the aberrations introduced by turbulence in the Earth's atmosphere. The most obvious manifestation of this is the twinkling of stars seen by the naked eye. Recent technological developments, such as compact and affordable deformable mirrors for compensating the optical distortions, mean that this technology is now being developed for more down-to-Earth reasons. This has opened up the possibility of using adaptive optics in smaller scale applications.In conjunction with researchers in Japan and Australia, I will develop adaptive optical fabrication systems that will be able to produce complex micrometre-scale structures with greater accuracy than was previously possible. With biologists in the University of Oxford, I will use adaptive optics to increase the capabilities of microscopes in imaging deep into thick specimens. This will enable biologists to learn more about the processes that occur within cells and the development of organisms. The aberration correction technology will also have use in other areas such as medical imaging, optical communications and astronomy.

I propose a new perspective and approach to understanding the interactions and interplay between quantum systems and their surrounding environments. By redrawing the boundary between what we term the system and what we term the environment, I shall provide a unified framework that will permit a breakthrough in the analysis of larger and more complex systems than presently possible. This will result in important new insights into both fundamental and applied physics across numerous settings. The behaviour of nanoscale systems comprising up to several thousand atoms is dominated by quantum physics, which can lead to surprisingly strong collective features. As an analogy, consider the cooperative behaviour of a crowd at a sports ground who sing in unison, allowing songs to be discerned despite the many voices. Likewise, in nanoscale systems quantum correlations can be shared across numerous constituent atoms, enabling them to behave as single entities in many situations. One of the most dynamic and exciting areas of scientific research over the past decade has been the quest to understand, control, and exploit these correlations for technological applications. Further progress in the field - which could lead to the next technological revolution - requires the development of an unprecedented level of understanding of the intricate quantum nature of matter. This is a formidable challenge, but also a central reason to engage in this fascinating area of research. A primary obstacle to exploiting quantum features of nanoscale systems arises due to the fact that no physical system can ever be completely isolated from the influence of its surroundings. The forces exerted by this large, fluctuating, and uncontrolled environment give rise to unwanted random variations in the system's properties, known as noise. Returning to our analogy, this is akin to each crowd member randomly singing a song with no regard to the songs of others, with the result (which would literally be noise!) that a listener would perceive no underlying structure. In the quantum realm noisy processes are particularly harmful. As well as obscuring the information we learn as we probe a system, interactions with the environment can destroy the very nature of the quantum state itself. From a quantum technology point of view, noise thus seems to render our system to be completely useless. This is the conventional view, at least. However, one of the exciting aims of my research programme is to give a viable alternative perspective on the role of noise in quantum processes. Imagine a crowd in which groups are singing different songs. Depending on how these groups form, compete, and evolve we may still perceive some structure beneath the din. In fact, by developing a new and unified understanding of the interactions between quantum systems and their environments I shall show that noisy processes can actually be harnessed to drive systems into exotic, robust, and useful quantum states. Indeed, a series of groundbreaking experiments have suggested that interplay between quantum effects and noise may unexpectedly exist in the natural light-harvesting networks of bacteria, algae, and plants. These systems are thus currently the subject of intense exploration and debate, motivated by the remarkable possibility that quantum physics may play an important role in the basic processes of life. Moreover, by understanding whether this helps natural systems to achieve robust and efficient solar-energy conversion, I aim to develop new design principles for quantum technologies that draw on solar light as a clean, sustainable, and efficient energy source. By tackling a core issue in quantum physics and a primary obstacle to exploiting quantum processes in the laboratory, my research will impact across a broad range of fields and technologies, paving the way to future applications of far-reaching social and economic importance as well.

Positrons are the antiparticles of electrons. They are produced in abundance in our Galaxy, and are readily obtained on Earth using accelerators or radioactive isotopes. When positrons come into contact with their matter counterparts, the pair annihilate in a pyrotechnic flash, releasing all their energy as pure light. This emitted light is detectable, and is strongly characterised by the environment the electron was in immediately prior to annihilation, making positrons a unique probe. As such, they have important use in medical imaging in PET (Positron Emission Tomography) scans, diagnostics of industrially important materials, and understanding the distribution of antimatter in the Universe. When low-energy positrons interact with normal matter, such as atoms, they pull strongly on the electrons and may even cause one of the electrons to `dance' around the positron, forming so-called positronium (as the positron and electron may annihilate, this may ultimately be a `dance to the death'). Such effects are known collectively as `correlations'. Correlations have a very strong effect on positron collisions with atoms and molecules. In particular, they can enhance the rate of positron annihilation by many orders of magnitude. They also make the accurate description of the positron-atom system a challenging theoretical problem. Proper interpretation of material science experiments, however, rely heavily on calculations that must fully account for the correlations. For example, to accurately interpret Positron Induced Auger Electron Spectroscopy, a powerful technique used to study defects and corrosion in materials, one requires the exact relative probabilities of annihilation with core electrons of various atoms. Moreover, accurate description of the positron-molecule system is required to help explain the origin of the strong annihilation signal from the galactic centre; to develop new spectroscopic PET-scanning methods for medical imaging, drug development and industrial diagnostics; and to advance antimatter-matter chemistry. Crucial in all cases is the ability of theory to accurately calculate the response of the atomic and molecular structure to the positron. A powerful method of describing the positron-atom or molecule system, which allows for the study and inclusion of correlations in a natural, transparent and systematic way, is many-body theory. In this method, complicated mathematical expressions that describe processes of interest, e.g., positron annihilation with an atomic electron, are replaced by series of relatively simple and intuitive diagrams, each of which represents a distinct correlation process. This programme of research proposes to develop new state-of-the-art diagrammatic many-body theory, and recently emerged revolutionary computational methods for high-precision calculations of positron annihilation with individual electrons in complex atoms and molecules. These computational methods will allow for the summation of millions of diagrams, completely unfeasible using the best existing brute-force methods, providing a powerful framework that can yield precision calculations in addition to keen insight. Moreover, the application of the methods will naturally extend to other important atomic and molecular properties and processes, required for tests of fundamental physics and development of quantum technologies. The unique and unrivalled calculational capability that this programme will develop will enable the most accurate interpretation of industrially important materials science experiments at recently launched international facilities; help provide fundamental insights into antimatter in the Galaxy; explain existing experimental results that remain crying out for theoretical explanation; advance Positron Emission Tomography technology and antimatter-matter chemistry; and overall, illuminate this intricate dance of matter and antimatter.

Almost all engineering systems and many biological ones contain components that are loaded and rub against one another, such as gears and bearings in machines and hip and knee joints in humans. This rubbing results both in friction, that wastes energy, and in wear and other forms of surface damage that lead to machine (and human) downtime, and the need for expensive repair and replacement. This whole field of research is called Tribology and is pivotal both in the quest for sustainability, including reducing CO2 emissions, and in improving the quality of our lives. In Tribology the effects of rubbing, such as frictional dissipation and wear, are perceived as macroscale phenomena and are traditionally studied by macroscale experiments and analysis. However they actually originate at the atomic and molecular scale, where the severe local stresses produced by rubbing cause restructuring of surface layers, while the molecules of lubricant in rubbing contacts interact with and protect surfaces. Thus to understand and so improve tribological systems we need an approach that spans the molecular, meso- and macro-scales. This will yield both information as to the origins of friction and surface damage - and unwanted phenomena are best tackled at their roots - as well as the ability to design macro-scale components such as lubricants, bearings, gears, engines and replacement joints that operate reliably and efficiently for as long as required. To meet this need, the proposed research will develop and apply advanced techniques to model rubbing contacts at all the necessary scales - atomic/molecular simulations of surfaces and lubricants, meso-scale modelling looking at structural evolution of surfaces due to rubbing, and macro-scale simulations of actual rubbing components such as bearings and engines. These simulations will be validated by experiments that also span the same range of scales, including direct observation of molecules in rubbing contacts. The most critical and innovative stage of this project, however, will be to link all these models together in to a single computer-based package. The result will be a set of modelling programs that can be used in many different ways; for example to explore the origins of tribological phenomena; to optimise lubricant surface and materials design; to predict performance of machines based on a combination of design and underlying atomic/molecular processes. Such an approach will give us tools both to understand in full tribological phenomena such as friction and wear and to enable effective "virtual testing", where new and novel designs, lubricants and surfaces can be combined and their effectiveness tested prior to recourse to time-consuming and expensive experimental development.