Research projects

Below is a list of potential thesis topics for students starting in October 2021. We have several fully funded studentships financed from a number of sources (EPSRC, STFC, Industrial Sponsorship, and College and Departmental Scholarships, etc.) for specific topics, and/or projects of our choice, and thus potential applicants may wish to indicate broad thematic areas in which they are interested when making an application. Students applying with their own sources of funding are welcome to apply for any of the listed topics.

Applications should be submitted via the main University webpage. Apply Here

Dr Chris Ballance

1. Quantum computing with trapped ions

Trapped-ion devices have demonstrated, on a small number of qubits, all the building-blocks required to build a quantum computer with precision better than any competing technology. The aim of this project is to develop and utilise a world-class intermediate-scale quantum computer that, by virtue of high-fidelity any-qubit-to-any-qubit entangling gates along with low error rates, will operate at a performance level currently unachievable in any other architecture.

This is a challenging project which will push the limits of laser technology, quantum/classical control techniques, and quantum algorithm design.

The project will involve both experimental and theoretical work, including:
- building an apparatus that uses a newly developed type of trapped-ion qubit
- obtaining precision coherent control over individual atomic ions
- developing and applying new theoretical tools to understand and optimise many-qubit couplings

For more information, please contact Dr Chris Ballance

2. Fast, high-fidelity entanglement via optical phase control

Trapped-ion devices have demonstrated, on a small number of qubits, all the building-blocks required to build a quantum computer with precision better than any competing technology. However the speed of these devices, limited by the entangling gates, has not increased commensurately. The aim of this project is to change this by exploiting optical phase control to significantly speed up trapped-ion entangling gates whilst also removing several currently limiting fundamental sources of error.

In preliminary work, we have recently demonstrated the first high-speed entangling logic gates for trapped-ion qubits [Schafer et al., Nature 555, 75 (2018)]. We achieved a fidelity of 99.8% for a 1.6µs gate time, close to the highest reported two-qubit gate fidelities of 99.9%, but more than an order of magnitude faster. Over the course of this project we will extend this proof-of-concept technique to demonstrate the first high-speed control of multi-qubit registers.

The project will involve both experimental and theoretical work, including:

- developing and numerically modeling phase-controlled fast entangling gate dynamics
- building a new apparatus optimised for high-speed multi-qubit entangling gates
- sophisticated classical control techniques to precisely control the optical interaction phase of multi-qubit registers

For more information, please contact Dr Chris Ballance

Dr Patrick Baird

DPhil Research Opportunity on Ultra-High-Q Microresonators for Optical Frequency Comb Generation

Ultra-High-Q microresonators are extremely powerful devices that allow confining enormous amounts of light into tiny micron-scale mode volumes. This enables the observation of nonlinear optical effects at low threshold powers, making microresonators ideal components for future integrated photonic circuits and for the next generation of optical computing.

A key application that utilizes nonlinear optics in microresonators is the generation of optical frequency combs. Optical frequency combs have been first developed 15 years ago and have become ubiquitous tools for spectroscopy, precision metrology and optical clocks. In 2005 optical frequency combs have been awarded with the Nobel Prize in Physics. Microresonators have recently shown to be promising candidates for shrinking optical frequency comb generators into chip-based devices for out-of-the-lab use [1]. However, the underlying physics of optical comb generation in microresonators is far from being fully understood and fundamentally different from conventional mode-locked laser comb generators [2].

There is opportunity for an Oxford D.Phil student to join a recently established research team at the National Physical Laboratory (NPL) to work on microresonator-based frequency comb generation. At present there are several research projects available both on the applied side of frequency comb generation in microresonators as well as on the fundamental research side with the goal of understanding the physics of the underlying comb generation process.

NPL provides an ideal environment for research on optical frequency combs with an existing infrastructure of optical atomic clocks and conventional frequency combs that can be used for future experiments.

[1] Del'Haye et.al, Optical frequency comb generation from a monolithic microresonator. Nature 450, 1214-1217 (2007)
[2] Kippenberg, Holzwarth, Diddams, Microresonator-Based Optical Frequency Combs. Science 332, 555-559 (2011)

For further information please contact either Dr Patrick Baird or Dr Pascal Del'Haye

Professor Andrea Cavalleri & Professor Paolo Radaelli

Breaking symmetry with light: ultra-fast ferroelectricity and magnetism from non-linear phononics

A collaboration between Prof. Paolo G. Radaelli and Prof. Andrea Cavalleri, who holds a joint appointment between
the Clarendon Laboratory and the Max Planck Institute for the Structure and Dynamics of Matter, (Hamburg).

Radaelli Cavalleri non linear graphic_0.png

Figure 1: schematic representation of non-linear photo-ferroicity. THz or far-IR ‘pump’ photons excite an IR-active mode (right), which is coherently coupled with a Raman mode (left). The rectified component of the Raman mode transiently generates ferromagnetism or ferroelectricity, which is probed coherently with a near-IR or visible light beam (top left).

The use of light to control the structural, electronic and magnetic properties of solids is emerging as one of the most exciting areas of condensed matter physics. One promising field of research, known as femto-magnetism, has developed from the early demonstration that magnetic ‘bits’ in certain materials can be ‘written’ at ultra-fast speeds with light in the visible or IR range [1]. More radically, it has been shown that fundamental materials properties such as superconductivity can be ‘switched on’ transiently under intense illumination [2]. Recently, the possibilities of manipulating materials by light have been greatly expanded by the demonstration of mode-selective optical control, whereby pumping a single infrared-active phonon mode results in a structural/electronic distortion along the coordinates of a second, anharmonically coupled Raman mode – a mechanism that was termed ‘nonlinear phononics’. Crucially, the Raman distortion is partially rectified, meaning that it oscillates around a different equilibrium position than in the absence of illumination. Very recently, it was realised that, under appropriate conditions, the rectified Raman distortion can transiently break the structural and/or magnetic symmetry of the crystal. Such symmetry breaking persist for a time corresponding to the carrier envelope of the pump, which can be less than a picosecond, and can give rise to the ultra-fast emergence of ferroic properties such as ferromagnetism and ferroelectricity. Through symmetry analysis and first-principle calculations, we have identified several promising ‘photo-ferroic’ materials that should display these effects, with potential applications in ultra-low-power information storage, ultra-fast electronics and many more.

This DPhil project will give the successful candidate the opportunity to pioneer this new field of research. Initial experiments on the candidate ‘photo-ferroic’ materials that we have already identified will be performed at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany. As a mode-selective pump, we will employ coherent laser radiation in the THz or far-IR range with sub-ps carrier envelopes, while the transient emergence of the ferroic properties will be probed with second-harmonic generation (SHG) and/or Faraday rotation of near-infra-red light. Later on in the project, changes in the crystal and magnetic structures of the materials will be probed with X-rays at free electron laser sources such as the European XFEL in Hamburg. Meanwhile, the candidate will develop search strategies for new classes of ‘photo-ferroic’ materials, based on symmetry and density functional theory calculations. He/she will develop the materials specifications in collaborations with crystal growers in Oxford and elsewhere, and will be involved hands on in all aspects of the design and realisation of the experiments and the data analysis.

The experimental part of this project will be predominantly based in Hamburg, so it is essential for the candidate to be willing and able to be based in Germany for extended periods during the DPhil.

[1] Femtomagnetism: Magnetism in step with light. Uwe Bovensiepen, Nature Physics 5, 461 - 463 (2009)
[2] See for example M. Mitrano,et al., ‘Possible light-induced superconductivity in K3C60 at high temperature’, Nature, 530, 461–464 (2016)
[3] Nonlinear phononics as an ultrafast route to lattice control, M. Först et. al., Nature Physics, 7, 854–856 (2011)

For further information please contact either Prof. Andrea Cavalleri or Prof. Paolo Radaelli

Professor Christopher Foot

1. Experiments with ultracold atoms and Bose-Einstein condensates

Professor Foot’s research group investigates the fascinating properties on ultracold quantum gases at temperatures of a few tens of nanokelvin. Samples are produced using laser light to cool atoms from room temperature and then confining them in a magnetic trap where evaporation leads to further cooling. These processes increase the phase-space density by many orders of magnitude to reach quantum degeneracy (Bose-Einstein condensate for atoms with integer spin). The research group in Oxford has pioneered new methods of trapping ultracold atoms using a combination of radiofrequency and static magnetic fields that is a very powerful tool for probing 2D quantum systems.

Research on `Investigating non-equilibrium physics and universality using two-dimensional quantum gases’ is funded by a new EPSRC grant [1]. Coherent splitting and matter-wave interference techniques enable comprehensive read out the quantum information from these systems to study fundamental questions such as how an isolated quantum system evolves towards equilibrium (or quasi-equilibrium states). We are working with theoretical colleagues to make detailed comparison with quantum statistical mechanics. Understanding the fundamental quantum physics of many-body system has important implications for quantum devices and technology based on them.

Future research directions include experiments on weak quantum measurements (sometimes called quantum non-demolition) on atoms in double-well potentials (bosonic Josephson junctions), squeezed states of the atoms and extensions to quantum gases that are a mixture of multiple species such a rubidium and strontium atoms.

[1] https://gow.epsrc.ukri.org/NGBOViewGrant.aspx?GrantRef=EP/S013105/1

For more information, please contact Prof. Chris Foot

2.Optical lattice clocks for fundamental physics and redefinition of the second

This is an experimental project, working with some of the UK’s best atomic clocks at the National Physical Laboratory. The clocks are based on strontium atoms, which are laser-cooled to a temperature of 1 µK, and then trapped in an optical-lattice dipole trap. The trapped atoms are probed using an ultra-stable clock laser, which is tuned in frequency to address a narrow optical transition at 429 THz. By measuring whether the clock laser excites the atoms or not, we can steer the laser to “tick” at a rate matching the narrow atomic transition frequency. Following this procedure, the clock laser can measure the passage of time to 18 digits of precision – enough to resolve the gravitational redshift from a change in height of just a few cm on the surface of the earth.

Already optical lattice clocks reach fractional frequency uncertainties and instabilities more than 100 times lower than the best caesium primary frequency standards. As a result, optical lattice clocks are a likely candidate for a future redefinition of the SI second. However, before such a redefinition, it must be shown that these systems can be engineered to run reliably, and that frequencies derived from such clocks are reproducible. We achieve this through real-time comparison of NPL’s clocks with others across Europe via optical fibre links, and across the globe via satellites including the soon-to-be-operational Atomic Clock Ensemble in Space (ACES). These ultra-precise clock-clock comparisons also provide valuable insight into many open problems in fundamental physics, underpinning the hunt for dark matter, tests for violations of relativity, and constraints on possible variations in fundamental constants. To extend the reach of clocks towards new applications, new techniques must be developed to overcome the current limitations on clock performance. This effort will be the focus of the current PhD placement, for instance by exploring how quantum entanglement can be leveraged to supress frequency instability arising from quantum projection noise by engineering ‘spin-squeezed’ states.

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For more information, please contact Dr Rachel Godun or Prof. Chris Foot

Professor Gianluca Gregori

1. High Energy Density Laboratory Astrophysics - Scaling the Cosmos to the Laboratory

We are looking for DPhil experimental/theoretical positions to study and simulate in the laboratory extreme astrophysical conditions. The research is focussed on the following themes:

1. Investigation of the equation of state of ultra dense matter as the one occurring in the core of giant planets (such as Jupiter and many exoplanets). The experimental work involves using high power laser facilities to compress the matter to densities above solid and then applying x-ray techniques to probe its microscopic state. Interested students can also focus their work onto theoretical topics involving strongly coupled and partially degenerate plasmas - which are particularly relevant for describing white dwarf structure.

2. The understanding of the generation and amplification of magnetic fields in the Universe. We are particularly interested at the role of turbulence (and dynamo) in producing the present day values of magnetic fields in cluster of galaxies. Experiments on large laser facilities are planned in order to simulate in the laboratory intra-cluster turbulence and measure the resultant magnetic field generation and amplification by dynamo.

3. Quantum gravity with high power lasers. The idea is to use high intensity lasers to drive electrons to very high accelerations and then observe effects connected to the Unhruh-Hawking radiation. The ideal candidate is expected to work in defining the required experimental parameters and the proposal for a future experiment.

Our group has access to several laser facilities (including the National Ignition Facility, the largest laser system in the world). Students will also have access to a laser laboratory on campus (currently hosting the largest laser system in the department), where initial experiments can be fielded. Further details can be found by browsing our research web-page http://www.physics.ox.ac.uk/users/gregorig/

For more information, please contact Prof. Gianluca Gregori

2.Laser experiments on novel hohlraum designs

Partial funding is available for a DPhil in Atomic and Laser Physics on experiments that support the Lawrence Livermore National Laboratory’s R&D projects in Inertial Confinement Fusion (ICF). Additional funding from University scholarship sources will be sought for suitably qualified candidates. The goal of ICF is to demonstrate fusion energy in the laboratory as a way towards clean and sustainable power for the next generations. In this project, we will be exploring ways in which to use low-density foams to mostly fill the interior of laser-heated cavities (also known as “hohlraums”) that are used to provide the x-ray needed to compress the deuterium-tritium fuel capsule used in ICF experiments. We will use novel foam configurations to try to control the hohlraum wall expansion and the capsule symmetry - a key requirement to achieve ignition. Experiments will be conducted at a major experimental laser facility in the US and UK (such as Omega or Vulcan) to test the most uncertain physics questions. The student will lead the experiment effort and provide a detailed analysis of the data.

For more information, please contact Prof. Gianluca Gregori

Professor Simon Hooker

Plasma accelerators

In a laser wakefield accelerator an intense laser pulse propagating through a plasma excites a trailing plasma wave via the action of the ponderomotive force, which acts to expel electrons from the region of the laser pulse. The longitudinal electric field in this plasma wakefield can be as high as 100 GV / m, more than three orders of magnitude larger than that found in conventional RF accelerators such as those used at CERN. Particles injected into the correct phase of the plasma wave can therefore be accelerated to energies of order 1 GeV in only a few tens of millimetres. Laser-driven plasma accelerators could therefore drive novel, very compact sources of particles and ultrafast radiation.
Theoretical and experimental work on plasma accelerators in Oxford is undertaken by a collaboration of research groups in the sub-departments of Particle Physics and Atomic & Laser Physics. For this reason applications to work in this area should be made to the sub-departments of Atomic & Laser physics AND to Particle Physics.
Our work in this area is undertaken in our new high-power laser lab in Oxford, and at national laser facilities in the UK and elsewhere. We have recently been awarded a £2M, 4-year grant from EPSRC to support our research programme.
Further information on our research can be found on the laser-plasma accelerator group website

We are offering two DPhil projects to start in October 2021, as outlined below.

1. X-ray sources driven in all-optical plasma channels

Conventional electron-beam-driven light sources (i.e. synchrotrons and free-electron lasers) use electron bunches with energies of a few GeV. An Oxford-Berkeley collaboration were the first to generate electron beams with comparable energy from a laser-plasma accelerator. Reaching this energy requires the driving laser pulse, which has an intensity of around 10^18 W / cm^2, to be guided over several centimetres — well beyond the distance over which diffraction occurs.
In the first GeV-scale experiments, the laser pulse was guided in a plasma channel — a gradient refractive index waveguide made from plasma — generated by a capillary discharge. The drawback of this approach is that the discharge structure can be damaged by the driving laser pulse. The Oxford group has recently developed a new type of plasma channel generated by auxiliary laser pulses. Since they are free-standing, these channels are immune to laser damage, and hence they are very promising stages for future multi-GeV plasma accelerators operating at kilohertz pulse repetition rates.
In this project we will investigate further developments of these hydrodynamic optical-field-ionized (HOFI) plasma channels, and their application to the generation of incoherent keV X-rays via the transverse oscillation of the electron bunch in the plasma wakefield.

2. Multi-pulse laser wakefield accelerators

In a laser wakefield plasma accelerator, a short, intense laser pulse is used to drive a longitudinal density wave (a ‘plasma wave’) in a plasma. The electric fields (which constitute a ‘laser wakefield') within this wave are about 1000 times greater than the accelerating fields employed in a conventional, radio-frequency accelerator — and hence laser-plasma accelerators can generate high-energy beams from a very compact accelerator stage. Laser-driven plasma accelerators have already been demonstrated to generated electron beams with energies of several GeV.
To date, most work has been done with single driving pulses. These must have an energy of order 1 J and a duration shorter than the plasma period, which is around 100 fs. These demanding parameters can be generated by Ti:sapphire laser laser systems. However, Ti:sapphire lasers have very low efficiencies (< 0.1%) and (at these pulse energies) are limited to pulse repetition rates below 10 Hz.
Many potential applications of laser-plasma accelerators — such as light sources and future particle colliders — require operation at much higher pulse repetition rates (at least in the kilohertz range) and much higher ‘wall-plug’ efficiencies. New types of laser are becoming available which can meet these requirements, but they generate pulses in the picosecond range, which are too long to drive a plasma wave. If the output pulses of these lasers could be modulated, with a modulation spacing equal to the plasma period, then they could be used to resonantly excite the plasma wave in a plasma accelerator. We have recently shown that this is possible in a proof-of-principle experiment which employed temporally-stretched Ti:sapphire laser pulses.
In this project we will investigate methods for modulating long, high-energy laser pulses to form a train of short, low energy pulses. We will investigate multi-pulse laser wakefield accelerators (MP-LWFA) driven in this way, and will seek to demonstrate electron acceleration in a MP-LWFA for the first time.

For more information, please contact Prof. Simon Hooker

Professor Dieter Jaksch

Solving non-linear PDEs on a quantum computer

This project is concerned with solving non-linear partial differential equations (PDEs) on a quantum computer. Recently, it has been shown that an exponential speedup in conventional multigrid (MG) methods for solving non-linear PDEs on a classical computer can be obtained via MG renormalization (MGR) methods [Journal of Computational Physics 372, 587 (2018)]. In this project, the DPhil student will implement MGR methods on a quantum computer focussing on industrially relevant problems in fluid dynamics. Based on current timetables for the future availability of quantum hardware (e.g. through our partnership with IBM), we expect our quantum algorithms to outperform classical computers within the next 3 – 5 years. Since non-linear PDEs are ubiquitous in all areas of science and technology, our method has the potential to leverage the use of quantum-enhanced algorithms in a broad range of real-world applications. The main tasks are:

(i) developing optimized implementations of algorithms for solving non-linear PDEs on existing quantum devices aiming to achieve an exponential speedup. This entails developing platform-specific algorithms mitigating their individual weaknesses such that a quantum advantage can be obtained. The student will consider quantum devices based on trapped ions and in particular the Q20:20 machine, as well as devices on IBM’s quantum computing network.

(ii) identifying industrially relevant applications where MGR methods on a quantum computer could help solving outstanding problems or improve the quality of existing solutions. This part of the project will be carried out in close collaboration with BAE Systems, who are interested in solving complex fluid dynamics problems that are modelled by non-linear PDEs.

For more information, please contact Prof. Dieter Jaksch

Dr Axel Kuhn

Demonstration of a cavity-based photonic entangler

Entanglement, in which two quantum systems can exhibit correlations that are greater than the limit allowed by classical physics, is one of the most intriguing predictions of quantum mechanics. Entanglement between remote atoms or ions is a key resource for quantum computing, and plays a central role in NQIT, the Oxford-led quantum technology hub.

We propose two schemes for entangling remote atoms: one probabilistic and one deterministic. In the probabilistic scheme, two distant atoms each emit a photon which are combined at the two input ports of a 50:50 beamsplitter. If the photons are detected at different output ports, then the atoms are projected into an entangled state. In place of a simple beam splitter, we also anticipate using more complex photonic networks [A. Holleczek, PRL 117, 023602 (2016)] in combination with active optical photon switching and routing. In the deterministic scheme, an atom emits a single photon which is reabsorbed by a second atom by running the emission process in reverse [J. Dilley, PRA 85, 023834 (2012)]. In doing so, the state of the first atom is entangled with that of the second. In both schemes, a high-finesse optical cavity is used to enhance the light-atom interactions.

Currently, we have two optical cavity experiments with random atom loading. The first phase of the project will be to build an optical dipole trap to permanently hold single atoms in the cavities. The feasibility of this approach has recently been demonstrated [D. Stuart, arXiv:1708.06672], and suitable fibre-tip and FIB-milled cavity mirrors are at present under development. The second phase will be to generate and quantify the entanglement between the two remote atoms using full Bell-state tomography.

Person specification

This is a highly challenging experimental project which will push the limits of laser and optical technology. It would suit a student with experience in atomic and laser physics and a keen interest in exploring quantum phenomena experimentally.

Work environment

The research team does encompass two postdocs and four graduate students which operate three laboratories dedicated to cavity-qed and atom-photon coupling in cavities at the Physics department of the University of Oxford. The work space is well equipped, comprising four vacuum chambers for studying atom-photon coupling in cavities, a large number of ECDL and fibre lasers for atom manipulation, a frequency comb for synchronously stabilising all laser and cavity frequencies, and a large battery of single-photon counters. The project builds on the current work by other graduate students in our group, atom-cavity coupling and strong cavity coupling.

The new student will directly contribute towards achieving cavity-mediated remote entanglement. All necessary apparatus exists within NQIT, including high-finesse cavities, vacuum chambers, and all lasers for trapping and driving the photon production process. Close support on a day-to-day basis will be provided by at least one Oxford PDRA for the duration of the project.

For more information, please contact Prof. Axel Kuhn

Professor Alexander Lvovsky

1. Superresolution imaging via linear optics in the far-field regime

This position is funded by a Marie Curie Innovative Training Network.

Rayleigh's criterion defines the minimum resolvable distance between two incoherent point sources as the diffraction-limited spot size. Enhancing the resolution beyond this limit has been a crucial outstanding problem for many years. A number of solutions have been realized; however, all of them so far relied either on near-field or nonlinear-optical probing, which makes them invasive, expensive and not universally applicable. It would therefore be desirable to find an imaging technique that is both linear-optical and operational in the far-field regime. A recent theoretical breakthrough demonstrated that “Rayleigh’s curse” can be resolved by coherent detection the image in certain transverse electromagnetic modes, rather than implementing the traditional imaging procedure, which consists in measuring the incoherent intensity distribution over the image plane. To date, there exist proof-of-principle experimental results demonstrating the plausibility of this approach. The objective of the project is to test this approach in a variety of settings that are relevant for practical application, evaluate its advantages and limitations. If successful, it will result in a revolutionary imaging technology with a potential to change the faces of all fields of science and technology that involve optical imaging, including astronomy, biology, medicine and nanotechnology, as well as optomechanical industry.

The group web site can be found here Group site

For more information, please contact Prof. Alexander Lvovsky

2. Optical neural networks

This position is funded by a Marie Curie Innovative Training Network.

Machine learning has made enormous progress during recent years, entering almost all spheres of technology, economy and our everyday life. Machines perform comparably to, or even surpass humans in playing board and computer games, driving cars, recognizing images, reading and comprehension. It is probably fair to say that a modern machine will perform better than a human in any environment it has complete knowledge of. These developments however impose growing demand on our computing capabilities, including both the size of neural networks and the processing rate. This is particularly concerning in view of the decline of Moore’s law.

The project is to implement artificial neural networks using optics rather than electronics. The training of neural network consists of linear operations (matrix multiplication) combined with nonlinear activation functions applied to individual units. Both these operations can be implemented optically using lenses, spatial light modulators and nonlinear optical techniques such as saturable absorption. However, one crucial element of the training procedure - so-called backpropagation - has so far remained elusive. Our group has developed an idea to overcome this obstacle and implement pure optical backpropagation in a neural network, thereby enabling the training that is practically electronics-free. We confirmed the viability of this approach by simulation. Our next goal – and the goal of this doctoral research project – is to set up an experiment and test the method in a practical setting.

The group web site can be found here Group site

For more information, please contact Prof. Alexander Lvovsky

Professor David Lucas

Chip-based quantum computing with trapped-ion qubits

Trapped ions constitute near-perfect qubits with unrivalled quantum logic performance. Microfabricated “chip” traps are a promising avenue for scaling up to the large numbers of qubits required for future quantum computers. We have previously demonstrated the highest precision elementary qubit operations, using chip traps (see papers here and here ), where the qubit control was by performed by microwave electronic techniques. We plan to combine these techniques with integrated optical elements (as recently demonstrated elsewhere, e.g. here and here) to provide a fully integrated and scalable platform for quantum information processing.

We are looking for a highly motivated first-class student to join these world-leading projects. For further information, please see our web page at www.physics.ox.ac.uk/users/iontrap

For more information, please contact Prof. David Lucas

Professor David Lucas & Professor Andrew Steane

Ion trap-integrated optical cavities for fast networked quantum computation

The Oxford team has recently demonstrated the generation of networked quantum entanglement with the best combination of speed and fidelity in the world see this article in Physics World. Entangling qubits via photons in this way opens the way to scalable quantum computing via a network of small processors. However, at present the speed of entanglement generation is limited by the fact that most photons emitted by the trapped-ion qubits are not captured. A solution to this problem is to use optical cavities, which can in principle increase the photon collection efficiency near unity, and permit MHz entanglement rates between the network nodes. The goal of this project will be to fabricate and test an integrated ion trap / cavity system, using cutting-edge microfabrication technology. Trapped-ion quantum computing forms the major hardware research area of the UK Quantum Computing and Simulation Hub

We are looking for a highly motivated first-class student to join these world-leading projects. For further information, please see our web page at www.physics.ox.ac.uk/users/iontrap

For more information, please contact Prof. David Lucas

Professor Peter Norreys

1. Maximising plasma turbulence in the hot spot of inertial fusion targets

The student will investigate, using relativistic fluid theory and Vlasov-Maxwell simulations, the local heating of a dense plasma by two crossing electron beams generated during multi-PW laser-plasma interactions with a pre-compressed, inertial fusion target. Heating occurs as an instability of the electron beams that drives Langmuir waves, which couple non-linearly into damped ion-acoustic waves and into the background electrons. Initial simulations show a factor-of-2.8 increase in electron kinetic energy with a coupling efficiency of 18%. By considering the collisionless energy deposition of these electron beams, we are able to demonstrate, via sophisticated radiation-hydrodynamic simulations, that this results in significantly increased energy yield from low convergence ratio implosions of deuterium-tritium filled “wetted foam" capsules, as recently demonstrated on the National Ignition Facility. This approach promises to augment the heating of the central hot spot in these targets, and is attractive as a complementary approach that of fast ignition inertial fusion.

The student will:
• Simulate (Vlasov or possibly particle-in-cell) parameter scan of the energy cascade. The question is how dependent are we
upon the electron energy, thermal spread, divergence, beam-to-background density ratio.
• Simulate the energy cascade process in an inhomogeneous plasma.
• Simulate energy cascade using finite beams.
• Help design experiments verifying the energy cascade process.

The student will also use machine learning to study the optimisation of the energy deposition process.

For more information, please contact Prof. Peter Norreys

2. Laser-Plasma Interaction Physics for Inertial Fusion and Extreme Field Science

Intense lasers have extraordinary properties. They can deliver enormous energy densities to target, creating states of matter in the laboratory that are otherwise only found in exotic astrophysical phenomena, such as the interiors of stars and planets, the atmospheres of white dwarfs and neutron stars, and in supernovae. The behaviour of matter under these extreme conditions of density and temperature is a fascinating area of study, not only for understanding of fundamental processes that are, in most cases, highly non-linear and often turbulent, but also for their potential applications for other areas of the natural sciences.

My team is working on:
• Inertial confinement fusion - applications include energy generation and the transition to a carbon-free economy and the development of the brightest possible thermal source for neutron scattering science
• New high power optical and X-ray lasers using non-linear optical properties in plasma
• Novel particle accelerators via laser and beam-driven wakefields - including the AWAKE project at CERN, as a potential route for a TeV e-e+ collider
• Unique ultra-bright X-ray sources

The understanding of these physical processes requires a combination of observation, experiment and high performance computing models on the latest supercomputers. My team is versatile, combining experiment, theory and computational modelling, including applications of machine learning - I can offer projects in all of these areas More specifically:

Project 1. I have applied for funding of a studentship via the EUROFusion Enabling Research grant “Foams as a Pathway to Energy from Inertial Fusion (FoPIFE)”. The student will help develop our understanding of wetted foam implosions using high power lasers as well as design and implement high energy laser experiments on at the Central Laser Facility and Ecole Polytechnique devoted to understanding the behaviour of laser-irradiated foam targets. We will know the outcome in December 2020 of the grant application.

Project 2. I have been awarded an STFC grant to implement a new optical diagnostic on the AWAKE run II experiment at the CERN laboratory, in conjunction with the John Adams Institute. Our aim is the visualise plasma wakefields as they evolve in the 10 metre long plasma column. This will be the first time that the structure of a beam-driven wakefield accelerator will be measured in the laboratory and promises exciting discoveries of the real structure of wakefields generated by the Super Proton Synchrotron beam (operating at 400 GeV). The student will help with the design and implementation of the oblique angle frequency domain holographic set-up, visualise the outcome and compare the data with state of the art computer simulations.

Project 3. I am about to submit a large collaborative grant application to UKRI-EPSRC on photon-photon scattering using intense laser pulses. The idea is to ‘polarise the vacuum’ using three intense laser pulses. The virtual electron-positron vacuum is then polarised by the electric field and behaves like a dielectric medium, with the generation of a fourth beam that has a distinct wavelength and direction. This will be the first tests of photon scattering in the low photon energy, strong field limit. It might provide tests of physics beyond the standard model. We expect to know the outcome of this application in June 2020.

For more information, please contact Prof. Peter Norreys

Dr Robert Smith

Single Impurity in a dipolar Bose-Einstein Condensate

A single impurity interacting with a quantum bath is a simple (to state) yet rich many-body paradigm that is relevant across a wide sweep of fields from condensed matter physics to quantum information theory to particle physics. The aim of this project is to experimentally explore this physics using the highly controllable platform of a ultracold bath of Erbium atoms in which potassium impurities can be imbedded. The special feature of Erbium atoms is their large magnetic dipole moments which result in long-range and anisotropic dipole-dipole interactions in addition to the short-range contact interactions more normally seen in cold atom systems. This opens new avenues in a range of topics from polaron physics to information flow in open quantum systems.

For more information, please contact Dr Robert Smith

Dr Sam Vinko

Exploring Quantum Plasmas with X-ray Free-Electron Lasers (XFEL)

The advent of high-brightness 4th generation free-electron laser (FEL) light sources has revolutionized our ability to study extreme states of matter with unprecedented precision and control. The addition of new high-repetition rate, high energy laser drivers to FEL beamlines, such as the Dipole laser at the high-energy-density (HED) beamline of the European XFEL, will allow for a host of new compression experiments in well-controlled high-energy-density conditions to be investigated. In particular, the capability to tune the inter-atomic spacing between atoms in plasmas and compressed solids to the point where inner-shell electrons start overlapping, interacting and hybridizing is of great interest as it constitutes a new quantum frontier in dense plasmas. This novel regime is one where quantum effects and correlation may be sustained up to very high temperatures, and can now be accessed for the first time in the laboratory.

DPhil projects exploring this quantum plasma regime are available, with a focus on theoretical, computational, or experimental research.

Our experimental efforts are undertaken at large-scale FEL facilities, such as LCLS in California and the European XFEL in Hamburg, where we deploy a range of techniques such as x-ray spectroscopy and scattering to understand how high-energy-density systems can be generated, and how they behave, in extreme conditions of temperature and pressure. For a flavour of the sort of work we do, some of our recent papers in this area are:

1) Humphries et al., Mapping the Electronic Structure of Warm Dense Nickel via Resonant Inelastic X-ray Scattering
2) Vinko et al.,Time-Resolved XUV Opacity Measurements of Warm Dense Aluminum
3) Van den Berg et al., Clocking Femtosecond Collisional Dynamics via Resonant X-Ray Spectroscopy

Our experimental work closely ties into computational modelling (density functional theory, collisional-radiative atomic kinetics), and the application of advanced statistical tools and machine learning to help interpret complex experimental measurements in large-dimensional spaces:

4) Kasim et al.,Building high accuracy emulators for scientific simulations with deep neural architecture search Also see reports on this work in Nature Physics and Science
5) Hollebon et al.,Ab initio simulations and measurements of the free-free opacity in aluminum
6) Kasim et al., Inverse problem instabilities in large-scale modelling of matter in extreme conditions

For more information, please contact Dr Sam Vinko

Professor Justin Wark

Joint Projects

Professor Wark will not be taking on students this year as main supervisor, but as he strongly collaborates with Professor Gianluca Gregori and Dr Sam Vinko may, if appropriate, act as second supervisor on certain of their projects

For more information, please contact Prof. Justin Wark