Research projects for October 2018

For courses which are still accepting applications, please visit the webpage on the Graduate Admissions website.

Studentships currently open for applications:

Professor Christopher Foot

Development of cold-atom sources for quantum technologies

This project is suitable for those with an interest in developing new apparatus that will be applied to practical devices. We have developed a compact source of cold rubidium atoms based on a novel (patented) design of magneto-optical trap and we are collaborating with a laser company based in Scotland (M Squared Lasers) to commercialise this work. In this project we will develop a compact source of laser-cooled strontium atoms working with that company and other interested parties. Strontium requires a considerably different approach to that used for rubidium and developing the experimental methods into a robust and reliable system is the primary task.

We anticipate that there will be considerable demand for sources of cold strontium since they are necessary for clocks that use atoms in optical lattices (strontium clocks are currently the world-leading technology), matter-wave interferometers (for which one of the strontium isotopes is very suitable), as well as more fundamental research work on ultracold molecules and quantum gases. In summary, strontium has considerable advantages for quantum technology but it is not (yet) used so widely as rubidium because it requires more complicated apparatus. The technical issues will be addressed in this project and the cold-atom source will be demonstrated by building a matter-wave interferometer. Collaborations with other research teams to demonstrate other applications are likely.

It is expected that this project will be fully supported by a studentship for 4 years. Further information is available from Professor Foot.

Email
c.foot1@physics.ox.ac.uk

Dr Axel Kuhn - NEW for 2018

Demonstration of a cavity-based photonic entangler - EPSRC funded

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 the proposed NQIT Q20:20 machine.

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. EPSRC eligibility criteria apply for this project, therefore only UK students witha funding status of "Home" are eligible for the position.

Work environment

The research team of Dr Kuhn 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. The deterministic entanglement scheme will be done in close collaboration with Almut Beige’s theory group in Leeds, who have developed a complete quantum description of the field inside a cavity, as well as devised cavity-cavity coupling protocols. All necessary apparatus exists within NQIT, including high-finesse cavities, vacuum chambers, and all necessary 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.

Further details from Dr Axel Kuhn.

Email
A.Kuhn@physics.ox.ac.uk

Applications must be made using the form on the Graduate Admissions website above. Please check back later if the form you need is not currently on the website, as there is a slight delay sometimes.

The following projects are currently closed for applications.

Dr Robert Smith - NEW

Superfluidity in the presence of dipolar interactions

In the study of many-body quantum systems, two of the key tuning parameters are the nature of interactions between the particles and the geometry in which the particles are confined.

proj01_0.png

This experimental DPhil project will use an ultracold gas of Erbium atoms, which due to their large magnetic dipole moment interact via longer range dipole-dipole interactions as well as the more usual contact interactions, to investigate the effect of long-range dipole interactions on superfluidity. The initial part of the project will involve designing and implementing a homogeneous quasi-2D trap for ultracold Erbium atoms before:

(1) Exploring the appearance and consequences of the ‘roton-like’ excitation spectrum that is expected in a dipolar gas for such a trapping geometry. This roton feature, characterised by a minimum in the dispersion relation of elementary excitations, is one of the defining attributes of superfluid liquid helium. This project will seek to directly measure the feature in a dipolar gas and then use the tunability of the cold atom environment to more fully map out and understand its consequences for superfluidity.

(2) Searching for a supersolid phase mediated by the long-range interactions. A supersolid phase is one in which there is both long range spatial ordering (like a solid) and long range phase coherence (like a superfluid).

Exploring Out-of-equilibrium many-body quantum systems

The scientific understanding of non-equilibrium phenomena is generally less advanced than that of the related equilibrium states. Consider for example an isolated many-body quantum system; there are many questions that are still far from answered: What determines whether a quantum system will equilibrate? How does a quantum system equilibrate? Does equilibration always mean thermalisation? What is the role of temperature? As well as being of fundamental scientific interest, these and many other questions will be crucial for future technologies such as quantum computing, where the dynamical response of the system to external operations is a key consideration. For example, dynamical considerations may place a speed limit on such operations.

proj02_0.png

This experimental DPhil project which forms part of the DesOEQ (Designing out of equilibrium many-body quantum systems) programme grant and will explore these issues using an ultracold gas of Erbium atoms. Topics to be covered will include studying the effect of long-range interactions on critical phase transition dynamics and studies of periodically driven systems and turbulence.

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. There is funding for a least one studentship on this project.

Email
p.baird1@physics.ox.ac.uk
pascal.delhaye@npl.co.uk

Professor Paolo Radaelli & Professor Andrea Cavalleri NEW for 2018

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) abstract pdf
[2] See for example M. Mitrano,et al., ‘Possible light-induced superconductivity in K3C60 at high temperature’, Nature, 530, 461–464 (2016). [more at this link].
[3] Nonlinear phononics as an ultrafast route to lattice control, M. Först et. al., Nature Physics, 7, 854–856 (2011).

Professor Christopher Foot

1. Experiments with ultracold atoms and Bose-Einstein condensates

Professor Foot’s research group investigate the fascinating properties on ultracold quantum gases at temperatures of a few tens of nanokelvin. The 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 enables the investigation of the properties of 2D quantum systems. We are setting up experiments to work with multiple atoms species, e.g. two isotopes of Rb, or Rb and K atoms, in which atoms of one species act as ‘quantum probes’ of the surrounding gas. This will enable us to read out the quantum information from these systems and investigate new aspects of quantum thermodynamics and statistical physics. This work on understanding the fundamental quantum physics of many-body system has important implications for quantum devices and technology based on them. We also plan to carry out experiments on the transport properties in 1D quantum systems. Experiments with cold atoms allow single particles to be imaged and their properties measured thus providing deep insights that are complementary to work on quantum matter in Condensed Matter.

Email
c.foot1@physics.ox.ac.uk

Professor Gianluca Gregori

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/

Prospective candidates are encouraged to contact Prof Gregori for further information.

Email
g.gregori1@physics.ox.ac.uk

Professor Simon Hooker

1. 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.

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.

Please note that applications to work in this area should be made to the sub-department of Particle Physics, as explained at http://lpax.web.ox.ac.uk/opportunities-graduate-research; this page also gives further information on DPhil projects which are available in this area.

2. Ultrafast lensless imaging with OPA-driven high-harmonic generation

The project involves the generation of high-order harmonics of ultrafast visible laser pulses, and the application of this radiation to coherent diffraction imaging (CDI). High-harmonic generation (HHG) is a fascinating process in which an intense, femtosecond-duration laser pulse strongly drives the valance electrons of an atom to induce a highly nonlinear polarization; these oscillating dipoles radiate the odd harmonics of the driving field to generate a coherent beam of harmonics extending from the visible into the soft X-ray region.

CDI is a new method for "lensless imaging,” which is invaluable in spectral regions (such as the X-ray region) in which conventional optics are not available. In essence, CDI works by recording the diffraction pattern of an object, and inverting this using fast phase-retrieval algorithms to deduce the original object.

We are interested in: (i) developing more efficient HHG sources, with improved properties, by using optical parametric amplifiers (OPAs) to optimize the wavelength of the driving laser; (ii) using the HHG beams for element-specific X-ray imaging of microscopic objects.

This work is supported by a 4-year research programme funded by EPSRC.

Further details are available at: http://lpax.web.ox.ac.uk/opportunities-graduate-research

Further details from Prof Simon Hooker.

Email
s.hooker1@physics.ox.ac.uk

Dr Axel Kuhn - NEW for 2018

Two PhD positions in Experimental Quantum Optics at the University of Oxford
Research group of Axel Kuhn (Atomic and Laser Physics, University of Oxford)

Please also see a global advert - see http://admin.euraxess.org/jobs/268354

Our research team at the University of Oxford offers positions for two doctoral students for a period of up to three years with an attractive salary. Both PhD projects are funded by a European Union Innovative Training Network (ITN). The aim of such ITNs is to provide structured, high quality, doctoral-level training in an academic collaborative network with strong involvement of industrial partners. Besides working on internationally competitive research projects in our laboratories, the successful applicants will attend ITN schools and workshops, have access to a professional skills training and development programme, and receive further scientific training at academic and industry partners in the network. The projects are embedded in the MSCA ITN “Light-Matter Interfaces for Quantum Enhanced Technology” (LIMQUET).

Hybrid quantum processing with atoms & photons in photonic networks
This project is aiming at the combination of integrated optics with single photons from strongly coupled atom-cavity systems. Besides demonstrating linear-optical quantum gates, multi-mode interferometers and photonic quantum walks, the idea of this new project is to investigate the usefulness of time-bin encoding within photons and to exploit atom-photon entanglement in the photon-emission process. The challenge will be to combine our existing single-photon emitters and the superconductive nanowire single- photon detectors with silica-on-silicon photonic chips carrying the LOQC networks. For doing so, a photonic switchyard consisting of electro-optic devices and fibre delay lines will be used to route the photons into the desired channels with the correct timing. Photon-photon correlation experiments are then going to be used to verify and demonstrate quantum supremacy of the networks under investigation. Furthermore we plan to investigate the feasibility of applying these photonic processing schemes in nano-scale light-matter interaction using plasmon-atom coupled system and near field nano-optics in collaboration with our project partners at the Université de Bourgogne.

Quantum entanglement of trapped neutral atoms
We propose two schemes for entangling remote atoms. In a probabilistic scheme, two distant atoms emit photons into high-finesse cavities that are eventually combined at a beamsplitter. Photon detections in different outputs then project the atoms into an entangled state. In a deterministic scheme, an atom emits a single cavity photon, which is reabsorbed by a second atom in a distant cavity. In doing so, the state of the first atom is entangled with that of the second. In both schemes, a high- finesse 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 a trap that permanently holds single atoms in the cavities. The second phase will be to generate and quantify the entanglement between two remote atoms using full Bell-state tomography. This project is based on three key technologies that we recently explored in our group, namely the trapping and manipulation of individual atoms in optical tweezers, high-finesse fibre-tip optical cavities and the quantum-controlled single-photon emission from coupled atom-cavity systems. Furthermore we plan to investigate how to apply this scheme to trapped ions with our project partner at the University of Sussex.

Person specification: These are highly challenging experimental projects which will push the limits of laser and optical technology. They would suit students with experience in atomic and laser physics and a keen interest in exploring quantum phenomena experimentally.

Given that the positions are funded by the European Commission on a H2020-MSCA-ITN, eligibility restrictions apply:
• Experience: Early-Stage Researchers (ESRs) shall, at the time of recruitment by the host organisation, be in the first four years (full-time equivalent research experience) of their research careers and not yet have been awarded a doctoral degree. Full-time equivalent research experience is measured from the date when a researcher obtained the degree which would formally entitle him or her to embark on a doctorate, either in the country in which the degree was obtained or in the country in which the researcher is recruited.
• Mobility Rule: at the time of recruitment by the host organisation, researchers must not have resided or carried out their main activity (work, studies, etc.) in the country of their host organisation for more than 12 months in the 3 years immediately prior to the reference date. Compulsory national service and/or short stays such as holidays are not taken into account.
• Each ESR will be supported by the project for a maximum of 36 months.
• All ESRs will take part in a secondment to another project partner for up to 30% of their appointment period.
• Mobility Allowances and Family Allowances (dependant on family circumstances) are payable to ESRs.

Work environment: The research team of Prof Kuhn 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 two projects build on the current work by other graduate students in our group, atom-cavity coupling and strong cavity coupling.
The new students will directly contribute towards achieving hybrid quantum processing with photons and atoms, and explore new schemes for cavity-mediated atomic entanglement. The projects will be pursued in close collaboration with our LIMQUET project partners in Dijon and Brighton. All necessary equipment is available, including high-finesse cavities, vacuum chambers, and the 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-based post-doctoral research assistant for the duration of the project.

Professor Ian Walmsley

Quantum photonics

Experimental quantum optics plays a key role in our growing understanding of the essential features of quantum physics, from foundational principles to consequences in information processing. To date, however, most experiments have been restricted to simple quantum systems composed of just one or two photons. A major aim for the field is developing methods to realise increasingly complex states from which remarkable properties are predicted to emerge. The Quantum Photonics team in the Ultrafast Quantum Optics Group works at the forefront of this challenge, using novel optical devices that enable the study of new large-scale quantum systems. We are developing photonic chips using the latest fabrication technologies that enable integrated quantum light sources and programmable multiport interferometers, optical fibre networks for time-domain manipulation of quantum light, and superconducting thin films that efficiently count single photons. We use these tools to study applications in quantum computation and metrology, as well as fundamental issues including the quantum-classical boundary and macroscopic quantum systems.

Potential research projects include:

* The quantum-classical transition in large optical networks: Optical fields provide a promising route to create quantum correlations across a network consisting of many nodes that span large distances. The preservation, manipulation, and measurement of multipartite quantum features, including entanglement, in these systems is an important challenge. We plan to develop practical theoretical tools and experimental methods to study the operation of large-scale quantum networks and how they differ from their classical counterparts.

* Quantum-enhanced biological sensing and imaging: Precisely designed quantum optical fields have potential to probe light-sensitive biological samples with unmatched precision. We will study the design of novel quantum-powered microscopes based on stimulated emission and phase-contrast imaging. The end goal is a laboratory demonstration of performance that exceeds the capability of a device using only classical optics.

* Direct quantum simulation and analogue computation: photonic coprocessors have potential to add purpose-built hardware to quantum computers. The fundamental properties of light enable unique construction of processors based on the quantum interference of non-interacting bosonic fields. We will study analogue computation based on the principles of boson sampling, and investigate the design of few-mode photonic simulators that can be used to study the physics of complex molecular and condensed matter systems.

We invite applications from outstanding, motivated students interested in joining our Quantum Photonics team to undertake a DPhil research project. You will gain expertise in experimental quantum optics, including knowledge of optics, lasers, integrated photonics, and quantum information. Your work will be carried out as part of a large team of experimental and theoretical quantum physicists, both in Oxford and collaborating institutions worldwide.

An overview of our research group is found at https://www2.physics.ox.ac.uk/research/ultrafast-quantum-optics-and-opti....

For further information please contact Professor Ian Walmsley.

Email
I.Walmsley@physics.ox.ac.uk

Professor David Lucas and Professor Andrew Steane

Quantum Computing with Trapped Ions, Lasers and Microwaves

Quantum computers offer the prospect of dramatic increases in information processing power, but this potential will only be realized if the qubits which hold the quantum information can be manipulated sufficiently precisely, and if the system can be scaled up to larger numbers of qubits.

At Oxford, we have recently developed the highest-performing qubit in the world, consisting of a single ion held in a microfabricated "chip trap". The qubit has a coherence time of nearly one minute, its quantum state can be prepared and read out with a fidelity of over 99.9%, and we can perform single-qubit quantum logic gates with an average fidelity measured to be 99.9999%. The key to achieving these results, which now define the state of the art, was the use of microwave techniques: the ion trap itself is a novel design, being the first to incorporate on-board microwave circuitry, and is built using a technology which is in principle scalable to much larger numbers of qubits. In related experiments we have recently demonstrated the highest-fidelity (99.9%) two-qubit quantum logic gate in the world, implemented using laser manipulation of the same type of qubit (hyperfine ground states in calcium-43 ions). Together, these results represent the first demonstration, in any qubit technology, of all fundamental qubit operations with sufficient fidelity for fault-tolerant quantum computing. As an application, we used our quantum logic gate to make the first test of Bell's Inequality with two different species of trapped atoms. We plan to scale our systems up to larger numbers of qubits by interfacing trapped-ion qubits using photonic qubits.

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

Email
d.lucas1@physics.ox.ac.uk

Professor Dieter Jaksch

1) Designing Out-of-Equilibrium Many-Body Quantum Systems

Many key existing and emerging technologies, ranging from switches in current computing and data networks to quantum devices for high-precision sensing, derive their functionality from out-of-equilibrium physics. As electronic devices become smaller, better understanding and control of this physics at the quantum level will become crucial to developing future technologies, and to address major challenges, such as developing energy-efficient switching and communications links. How to exploit the advantages of increasingly complex devices in the quantum regime and in the presence of noise and decoherence is intrinsically an issue of out-of-equilibrium many-body quantum physics. It is therefore crucial to put methods in place now that will underpin the design of out-of-equilibrium quantum systems, and lead to novel quantum devices.

This theoretical DPhil project will be attached to the EPSRC programme grant DesOEQ which aims to explore, understand, and design out-of-equilibrium quantum dynamics that are relevant for future technologies, using quantum simulators with atomic gases in optical potentials. These simulators offer a unique level of controllability on a microscopic level, where interactions and trapping potentials are quantitatively understood from first principles. Their size and time scales make it possible to directly image and manipulate the system on the level of a single atom, as well as to track and control dynamics in real time. The DPhil project will specifically consider steady-states of driven, dissipative ultracold atomic systems with the aim of reaching otherwise inaccessible quantum phases [1,2]. For instance, the project will study the dynamics near transitions between different phases of the driven Hubbard model investigated in [1] and how the physics is affected when coupling the system to a dissipative bath.

[1] J. R. Coulthard, S. R. Clark, S. Al-Assam, A. Cavalleri, and D. Jaksch, Phys. Rev. B 96, 085104 (2017)
[2] F. Görg, M. Messer, K. Sandholzer, G. Jotzu, R. Desbuquois, T. Esslinger, arXiv:1708.06751 (2017)

2) Long-ranged interactions in ultracold molecules

Many new applications in quantum science and technology have emerged from the full quantum control of ultracold atoms. Molecules offer even greater possibilities owing to their rich internal structure, controllable long-range dipole-dipole interactions and stronger couplings to electric and microwave fields. However, quantum control of molecules is fundamentally different from controlling atoms and needs to be developed in order to exploit their potential. The EPSRC programme grant QSUM develops this control through a coherent research programme of interconnected experimental and theoretical projects.

This theoretical DPhil project is attached to the QSUM grant and will investigate the physics of arrays of ultracold polar molecules interacting via long-range dipole-dipole potentials. These systems promise to be a fundamentally new tool for understanding the quantum physics of strongly correlated many-body systems. For example, such systems will allow us to understand the exotic quantum phases of dipolar quantum gases and to simulate lattices of interacting spins. They will reveal fundamental aspects of quantum magnetism, and allow us to explore new regimes of superfluidity, including stable topological phases relevant to quantum information processing. To address these questions this DPhil project will develop theoretical methods and algorithms based on tensor network theory to describe long-ranged molecular interactions in lattice systems. These will then be used to study the quantum phases of molecular arrays and their potential as a quantum technologies platform.

Email
d.jaksch1@physics.ox.ac.uk

3) NQIT quantum simulation project:

This project will contribute towards work package 7 (WP7) of NQIT. The research in WP7 investigates how the Q20:20 and other early quantum computing devices could be used as a quantum co-processor in high performance computing (HPC). We currently focus on algorithms used in scientific research computing. Specifically, we have been investigating a quantum co-processor for dynamical mean-field theory (DMFT) which is used in physics and in materials science for modelling strongly correlated systems and now extend these studies to non-equilibrium density functional theory (DFT). The main idea is to split algorithms into a linear part that can efficiently be solved by Q20:20 while performing non-linear and self-consistency feedback loops using conventional HPC. In the case of DMFT the problem can be rewritten as a linear quantum impurity lattice problem whose Hamiltonian parameters coupling the impurity to bath sites need to be determined self-consistently.

The student on this project will be tasked with

(i) investigating variations of the protocols presented in arXiv:1510.05703 and arXiv:1606.04839 with the main goals of optimizing the quantum part of the algorithm for early quantum computing architectures and minimizing the amount of quantum resources required for achieving non-trivial hybrid DMFT simulation results. This work will ensure that the quantum resources provided by early quantum processors are exploited to their fullest potential.
(ii) studying the influence of imperfect implementations of the quantum algorithms in (i) on the accuracy of the DMFT simulation results. This work will ideally use an early quantum device accessed through the NQIT hub. Its major aims will be to calculate the error thresholds for obtaining reliable simulation results and to determine which of these algorithms are best suited for early quantum computing implementations.

Email
d.jaksch1@physics.ox.ac.uk

Professor Peter Norreys

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 – please contact me to discuss your interests and let’s take it from there.

Email
p.norreys1@physics.ox.ac.uk

Professor Ian Walmsley

Cavity opto‐mechanics: from quantum foundations to quantum technologies

Cavity quantum opto-mechanics is one of the newest and fastest growing areas of quantum science internationally and was recently noted by the Nature Publishing Group as a milestone in physics [1]. Central to opto-mechanics is radiation pressure (the force exerted by simply the reflection of light), which is used to control the motion of micro‐ or nano‐fabricated mechanical resonators. Using this interaction in combination with the techniques of quantum optics provides a route to experimentally generate quantum states of motion at a truly macroscopic scale. This rich avenue offers significant potential to contribute to both fundamental and applied science, allowing quantum-enhanced weak force sensing with unprecedented precision, and even offering one of the most promising routes to observe quantum gravitational phenomena with a table-top experiment [2,3]. Specific DPhil projects can be tailored to the student’s interests and can focus in one of two directions: (i) to experimentally develop techniques to generate and probe non-classical states of motion [4,5] to empirically explore fundamental physics, such as potential quantum gravity phenomena [2,3], or (ii) to utilise quantum states of motion to develop ultra-sensitive force sensors that can play a key role in the next generation of quantum technologies.

Successful DPhil applicants will be part of a vibrant international team of researchers working in close collaboration with several research groups in Oxford, London, and overseas, including Australia, Germany, Japan, and the United States. You will gain an expertise in experimental quantum optics, lasers, cryogenics, as well as simulation and theoretical modelling in a number of different areas of physics. You will also have the opportunity to spend some of your DPhil abroad to work with our collaborators. Recent opto-mechanics graduates have went on to pursue exciting careers in Google, NASA, and IBM, as well as becoming internationally leading academics.

[1] http://www.nature.com/milestones/milephotons/full/milephotons23.html
[2] R. Penrose, General Relativity and Gravitation 28, 581 (1996).
[3] I. Pikovski, M. R. Vanner, M. Aspelmeyer, M. S. Kim, and C. Brukner, Nature Physics 8, 393 (2012).
[4] K. C. Lee, etal., Science 334, 1253 (2011).
[5] M. R. Vanner, M. Aspelmeyer, M. S. Kim, Physical Review Letters 110, 010504 (2013).

For further information on this DPhil opportunity please see our group webpage

https://groups.physics.ox.ac.uk/QMLab/

Dr Sam Vinko - two new projects for 2018

1. Unravelling complex processes in high-energy-density plasma physics via machine learning

Large-scale experiments in high-energy-density plasma physics relevant to inertial confident fusion and astrophysical research rely on complex computational modelling in high-dimensionality parameter spaces for the interpretation of experiment results. These spaces are generally too large for all the possible outcomes to be investigated systematically using grid-search techniques, which makes it difficult to find regions of parameter space that are particularly favourable to some desired outcome. This project will seek to apply a range of methods in machine learning to build an algorithm capable of learning how to robustly interpret experimental measurements within the context of a given plasma model (applied primarily to x-ray spectroscopy, radiography and scattering diagnostics), and to guide the design of large-scale experiments based on specific, desired outcomes.

Candidates must be willing and able to travel to the USA and across the EU on a regular basis as part of this project.

For further information please contact Dr Sam Vinko:

Email
s.vinko@physics.ox.ac.uk

2. Ionization dynamics of metalloproteins driven by intense free-electron lasers

This project aims to investigate the mechanisms leading to ultra-fast ionization and electron damage in metalloprotein systems on femtosecond time scales using bright x-ray free-electron lasers. Experiments at the Linac Coherent Light Source in California (https://lcls.slac.stanford.edu), the European XFEL in Germany (https://www.xfel.eu), and other facilities around the word will be complemented by computational work using a range of large-scale ab-initio and atomic kinetics simulations. Experimental diagnostics will include x-ray spectroscopy, x-ray scattering and coherent diffraction imaging of metalloproteins to study the transition from weakly ionized systems, of relevance to biology and chemistry, to highly ionized, hot plasmas relevant to solar physics investigations. We anticipate there will be abundant opportunities for interdisciplinary work spanning across physics, chemistry and biology.

Candidates must be willing and able to travel to the USA and across the EU on a regular basis as part of this project.

For further information please contact Dr Sam Vinko:

Email
s.vinko@physics.ox.ac.uk

Professor Ian Walmsley

Attoscience and Strong Field Physics

Recently, nonlinear frequency conversion has been extended to provide access to coherent extreme ultraviolet (XUV) and soft x-ray radiation. This has enabled experiments routinely performed at synchrotron and free-electron laser facilities to be moved into a compact laboratory environment, and the underlying physics has given birth to attoscience. This emerging field concerns the observation of electron and atomic dynamics at the microscopic level, where the timescale is measured in attoseconds (10-18 s). Such fundamental measurements will have a wide reaching impact throughout the sciences, and potential applications include computation, energy harvesting and healthcare. The Attoscience and Strong Field Physics section of the Ultrafast Group are engaged in all aspects of attoscience research from the production of energetic few-cycle laser pulses, to the generation, all-optical characterization and use of XUV radiation.

Applications are invited from outstanding students interested in joining the Attoscience and Strong Field Physics team to pursue a DPhil research project. You will work with an advanced laser system on a daily basis and gain a deep understanding of ultrafast optics, XUV technology and state-of-the-art imaging techniques. In addition to a strong experimental focus, you will also have the opportunity to develop strong computational skills.
The main research activities are summarised at https://www2.physics.ox.ac.uk/research/ultrafast-quantum-optics-and-opti.... For further information please contact Dr. Patrick Anderson or Professor Ian Walmsley.

Email
I.Walmsley@physics.ox.ac.uk

Professor Justin Wark

Studying High Pressure Matter with X-Ray Lasers

An opportunity exists for a DPhil project in the Physics Department at the University of Oxford to use the brightest X-ray source on the planet to study the response of matter to pressures normally only found towards the centre of planets. The student will work under the supervision of Professor Justin Wark in the sub-department of Atomic and Laser Physics. The project, funded by Lawrence Livermore National Laboratory in California, will entail both an experimental and theoretical study of matter under extreme conditions. On the experimental side, the student will use intense optical lasers to subject matter to many millions of atmospheres for timescales in the sub-nanosecond regime. In conjunction, the most intense x-ray laser on earth - the Linac Coherent Light Source at SLAC, will be used to obtain few-femtosecond single-shot diffraction images as the matter deforms or forms new phases. The experiments will be complemented by both classical molecular dynamics simulations, and by ab initio density functional theory calculations. The work builds on previous successful research recently published at the highest level (Science, 342, 220 [2013]). Full funding exists (fees and stipend) for successful UK or EU candidates for a period of 3.5 years. Interested candidates should have a upper-second or first class degree (or equivalent) in Physics, be interested in both experimental and theoretical physics, and be willing to spend some short periods in the US for experiments and collaborations. Enquiries can be made to Professor Justin Wark.

Email
j.wark1@physics.ox.ac.uk