# Research projects for 2015

### Dr Patrick Baird and Dr Patrick Gill, NPL

We have a number of projects involving laser-cooled ions and atoms. These are principally aimed at new frequency standards in the optical region, i.e., the development of new optical clocks. There are opportunities for Oxford doctoral students to conduct research in these areas in collaboration with NPL.

### A laser-cooled, single ion optical clock

The 2S1/2 – 2F7/2 octupole transition at 467 nm in 171Yb+ is hugely forbidden by quantum mechanical selection rules, and as a result has extremely long lifetime against decay, and a correspondingly ultra-narrow natural linewidth (~ nHz). By electromagnetically trapping a single 171Yb+ ion and laser cooling it to about 1 mK under ultra-high-vacuum (UHV) conditions, it is possible to prepare an ion virtually at rest in an isolated environment. The narrow octupole transition can then be probed with a very stable, narrow-linewidth semiconductor laser to provide a highly accurate atomic clock. In addition, by simultaneously probing a second optical clock transition at 436 nm – this time an electric quadrupole transition: 2S1/2 – 2D3/2) using the same 171Yb+ ion, the frequency ratio between the two transitions can be accurately determined; this gives a very sensitive measure of any possible temporal variation in the fine structure constant, α. There is opportunity for an Oxford doctoral student to join an NPL research team developing these ideas. Experimental techniques used in this project include ion trapping, laser-cooling, laser stabilisation using optical cavities, single ion quantum detection and UHV systems.

The project offers funding through an EPSRC CASE award.

In the first instance, please contact: Dr Patrick Baird.

### Cold Atoms in an Optical Lattice Potential

There is an opportunity for an Oxford student to undertake research on the NPL neutral lattice clock project. This research involves holding neutral strontium atoms in an optical lattice field in order to probe a clock transition; this offers potential for a future high-accuracy optical frequency standard and clock. Atomic clock systems bring together many aspects of experimental atomic physics research and in particular this project brings together magneto-optical trapping of neutral atoms together with cooling techniques, involving both broad- and narrow-line cooling transitions to cool clouds of neutral Sr atoms to microKelvin temperatures. The use of a “magic wavelength”, optical lattice trap, formed by counter-propagating laser beams, holds the atoms in space without perturbing the clock transition. The development and stabilisation of ultra-narrow linewidth lasers which are necessary for excitation of the clock transition will also be an essential part of the project.

Please click here for further details |
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http://www.npl.co.uk/science-technology/time-frequency/research/optical-frequency-standards/trapped-ion-optical-frequency-standards |

The project offers the possibility of funding through an EPSRC CASE award; for non-UK applicants there is a Marie-Curie funding for which a separate application is necessary - see next section for more information.

In the first instance, please contact: Dr Patrick Baird.

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P [dot] Baird1 [at] physics [dot] ox [dot] ac [dot] uk 01865 272 204 |

### Marie-Curie Early Stage Researcher

#### Cold neutral atom optical lattice clocks

There is a vacancy for a Marie-Curie Early Stage Researcher within the EU Initial Training Network project Future Atomic Clock Technology (FACT) co-ordinated by the University of Birmingham, to undertake experimental research on cold atom optical lattice clocks at the UK National Physical Laboratory (NPL) under a DPhil (PhD) postgraduate studentship at the University of Oxford.

The post will be held within the group of Prof. Patrick Gill at NPL, in collaboration with Dr. Patrick Baird at the University of Oxford. The duration is 36 months, starting as soon as possible after 1st April 2014, and certainly by 1st October 2014. The salary is in line with the EC rules for Marie Curie grant holders (ITN Early-Stage Researchers), and is subject to a country-specific cost of living adjustment. The gross salary* is €51,000 per annum plus a monthly mobility allowance depending on family circumstances. Additional funds are also available to cover the DPhil tuition costs and participation in Marie-Curie network research and training activities. (*Net salary will result from deducting compulsory social security contributions as well as direct taxes, from the gross amount.)

To be eligible for the Marie Curie ESR grant, the candidate should have less than 4 years research experience (including previous postgraduate training). Further, the candidate must not have spent more than 12 months in the UK in the 3 years prior to appointment. The position is open to non-UK EU applicants and also non-EU applicants (subject to FACT network quota limits in the latter case). Details are given at: http://ec.europa.eu/research/mariecurieactions

The thesis will cover experimental research in cold atom physics, whereby an ultra-narrow optical transition in cold neutral strontium atoms held in an optical lattice field are probed by an ultra-stable laser to provide a high-accuracy optical clock frequency, with potential for redefinition of the SI second. This project brings together magneto-optical trapping of neutral atoms together with laser cooling techniques, to cool clouds of neutral Sr atoms to micro-Kelvin temperatures above absolute zero. A “magic wavelength” optical lattice trap, formed by counter-propagating laser beams, holds the atoms in space without perturbing the clock transition. Development of ultra-narrow linewidth lasers to probe the clock transition is also an essential part of the project.

During the last two decades, atomic clocks and frequency standards have become an important resource for emerging quantum technologies, with impact ranging from satellite navigation to synchronisation of high speed communication networks. Optical atomic clocks are now demonstrating sensitivities at the few parts in 1018, opening up applications in fundamental physics, in “relativistic geodesy”, where ultraprecise clocks sense the general relativistic gravitational redshift (with application to oil and mineral exploration, and climate research), and in future satellite and deep space navigation. However, the underlying technologies associated with such clocks are still primarily lab-based. The FACT ITN research training programme covers all aspects of optical atomic clock technology, from the cold atom reference and ultra-stable lasers to frequency comb synthesis, precision frequency distribution and commercial system technology.

Further details on NPL, the University of Oxford research, and the FACT ITN can be found at:

http://www.npl.co.uk/science-technology/time-frequency/research/

http://www2.physics.ox.ac.uk/study-here/postgraduates/atomic-and-laser-p...

http://itn-fact.eu/

Candidates should submit an application letter and CV to NPL in parallel with a standard Oxford Atomic & Laser Physics research application ( http://www2.physics.ox.ac.uk/study-here/postgraduates/atomic-and-laser-p... ) to the Graduate Admissions Office, identifying the NPL EU Marie-Curie studentship in answer to the question on intended source of funding. The closing date for the application to NPL is 28th February 2014, but candidates should submit their application to Oxford as soon as possible. Candidates are also reminded that they need to satisfy the University of Oxford postgraduate research entrance requirements before an offer of the NPL position can be made.

Additional information can be obtained from:

P [dot] Baird1 [at] physics [dot] ox [dot] ac [dot] uk |

Patrick [dot] gill [at] npl [dot] co [dot] uk |

### Dr Laura Corner

### Resonantly Enhanced Multiple Pulse Laser Plasma Acceleration

The Lasers for Accelerators (L4A) group at the John Adams Institute for Accelerator Science is a versatile team focused on several areas of cutting edge research in the boundary between accelerators and lasers. In particular, the group is developing an new method for laser plasma acceleration, involving driving the plasma oscillation with trains of low energy laser pulses. This would enable the use of tabletop laser for plasma acceleration, rather than the use of national scale facilities. In this context, the L4A group is focusing on developing a suitable laser to drive plasma oscillations by a train of laser pulses in order to build a 1 GeV electron accelerator operating at 1 kHz. A PhD student project is available in this area within the JAI. The student would be working on developing new laser technologies in our laser lab in Oxford, including investigating methods of shaping a pulse train to efficiently excite a plasma oscillation and methods of coherent combination and enhancement of photonic crystal fibre laser pulses. In conjunction with this work, the student would also be working on diagnostic methods for measuring the amplitude of plasma oscillation and using this to evaluate the best laser pulse trains for excitation. The project would therefore be primarily experimental in nature, and suit a student with an interest in laser or accelerator science. However, there is scope for the student to develop theoretical and simulation work, especially on the plasma and diagnostics side of the project. The student would be based in Oxford, but there are opportunities to present work at international conferences and attend specialist workshops abroad. We welcome enquiries from candidates who may be interested in this project.

Supervisors: Dr Laura Corner and Dr Roman Walczak

http://www.physics.ox.ac.uk/l4a

Application deadline: January 10th

Funding source: STFC studentship for eligible students

Duration: 3 years

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l [dot] corner1 [at] physics [dot] ox [dot] ac [dot] uk | 01865 273470 |

### Professor Christopher Foot

### Single-atom imaging of strongly correlated quantum systems at nanokelvin temperatures

(keywords: Bose-Einstein condensation, laser cooling of atoms, and quantum simulation)

This project is part of a programme of work in the Ultra-cold Quantum Matter group to carry out quantum simulation of strongly correlated systems--such systems with a high degree of quantum entanglement are computationally hard to investigate and therefore the exciting new approach of making analogues of such systems using cold atoms is very effective. In Oxford we have developed an apparatus to produce rapidly rotating clouds of ultracold atoms that are equivalent to correlated systems in ultra-high magnetic fields. We have also built an experimental apparatus for trapping quantum gases of rubidium and potassium at nanokelvin temperatures. By detecting the quantum state of individual atoms we shall be able to readout the state of the system. This research combines techniques of laser cooling and trapping of atoms with high numerical aperture optical imaging system. The experimental work is funded by an EPSRC grant, and further details of the original proposal may be found at: http://gow.epsrc.ac.uk/NGBOViewGrant.aspx?GrantRef=EP/J008028/1

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c [dot] foot1 [at] physics [dot] ox [dot] ac [dot] uk | +44 (0) 1865 272256 |

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http://www.physics.ox.ac.uk/users/foot/ |

### 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/gregrig/

Perspective candidates are encouraged to contact Dr Gregori for further information.

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http://www.physics.ox.ac.uk/users/gregrig/ |

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g [dot] gregori1 [at] physics [dot] ox [dot] ac [dot] uk | +44 (0) 1865 282639 |

### Professor Simon Hooker

### Multi-pulse laser wakefield acceleration

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.

The laser wakefield accelerator (LWFA) has many potential applications. However, most of these - including, in the long term, laser-driven particle colliders - will require the accelerator to operate at much higher pulse repetition rates than is possible with the Ti:sapphire lasers used today.

An interesting new approach being developed by a collaboration between groups in the sub-departments of Particle Physics and Atomic & Laser Physics: multi-pulse LWFA, in which a train of low-energy laser pulses drives the plasma wave. If the pulses in the train are spaced by the plasma period then the wakes excited by each pulse interfere coherently to form a large-amplitude wave at the back of the pulse train. The advantage of this approach is that it opens the possibility of using novel laser systems - such as thin-disk and fibre lasers - which can operate at very high pulse repetition rates and with excellent overall efficiency.

Multi-pulse LWFA is a new idea and many interesting questions remain to be solved. This project offers scope for numerical simulations aimed at understanding the limitations of this approach and experimental work to demonstrate its potential.

For further details see: http://www2.physics.ox.ac.uk/research/plasma-accelerators-and-ultrafast-....

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s [dot] hooker1 [at] physics [dot] ox [dot] ac [dot] uk | +44 (0) 1865 282209 |

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http://www.physics.ox.ac.uk/contacts/people/hooker |

### Professor Simon Hooker

### Ultrafast lensless imaging with OPA-driven high-harmonic generation

An intense laser pulse interacting with the atoms or molecules of a gas can drive a highly nonlinear polarization which in turn generates coherent radiation at harmonics of the laser. This high-harmonic generation (HHG) process can generate ultrafast (in the attosecond range) pulses of radiation in the important soft x-ray spectral region, with potential applications in ultrafast imaging and in time-resolved science.

The efficiency of HHG is low unless steps are taken to phase-match or quasi-phase-match (QPM) the generation process. The wavelength of the driving laser is also important in determining the brightness and range of photon energies which can be generated. Our group has developed several techniques for QPM and demonstrated that these methods can increase the energy in the harmonic beam by more than an order of magnitude.

In this project we will use femtosecond optical parametric amplifiers (OPAs) to determine the optimum driving laser wavelength for generating x-rays of a given photon energy. We will also investigate a new QPM technique based on modulation of the polarization state of the driving laser in a birefringent waveguide.

The bright x-ray beams generated by these methods will be used for coherent diffraction imaging. This method images objects without conventional optics (which are not available at these wavelengths); it does so by recording the intensity diffraction pattern of the object and using sophisticated algorithms to overcome the "phase-retrieval problem" to deduce the object. Using a wavelength-tunable x-ray source we will seek to image specific elements in a sample, and as a test of these ideas we will the size and shape of particles formed in precipitation-strengthened Al alloy.

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

Further information available from: http://www2.physics.ox.ac.uk/research/plasma-accelerators-and-ultrafast-....

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s [dot] hooker1 [at] physics [dot] ox [dot] ac [dot] uk | +44 (0) 1865 282209 |

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http://www.physics.ox.ac.uk/contacts/people/hooker |

Application deadline: n/a

Duration: 4 years

### Professor Dieter Jaksch

### 1) Simulation of two-dimensional strongly-correlated quantum systems using high-performance tensor network theory algorithms

Tensor network theory (TNT) provides efficient and highly accurate methods for simulating many-body quantum systems, which cannot be represented exactly for all but the smallest systems due to the exponential growth of the number of parameters required with system size. The many-body wave function, and the operators that act on them, are represented as a network of tensors (multi-dimensional arrays of numbers) which is manipulated by performing a series of tensor manipulations such as reshaping, contracting and factorising. This computational/numerical DPhil project focusses on developing new algorithms for treating two-dimensional systems that utilise TNT, and will be added to the existing TNT software library. This high-performance library has been developed in our group for the last two years, and already has many users. The project will provide algorithms that are the first of their kind freely available as part of a software library, and will be used not only by members of our group, but research groups throughout the UK. The code is being developed in C, with OpenMP and MPI also being used to implement a hierarchical parallelisation scheme. The DPhil student will collaborate with members of our group to design routines that can be used by them to solve physics problems. The student will also have the chance to work with scientific software engineering experts who provide us with advice on producing high-quality sustainable software and on optimising our codes for running on large–scale supercomputers, such as the national supercomputing cluster ARCHER.

### 2) Optically steering, manipulating and cooling strongly correlated electron systems

In the past decade there have been pioneering experiments which have shown how laser light can manipulate, measure and selectively cool not only atoms or ions, but also single modes in macroscopic opto-mechanical devices. A major long-term aim in our group, in collaboration with Prof. Andrea Cavalleri Oxford/Hamburg experimental group, is to apply these techniques to strongly correlated electron systems such as Mott insulators and cuprate superconductors. Broadly this work plans to identify and realize "hidden" phases of materials, that are metastable out-of-equilibrium states which only exist while the system is driven. A key example of this would be to devise techniques to engineer the coupling of a stacked cuprate material to a surrounding cavity so that emissions into the cavity mode result in the cooling of superconducting phase fluctuations. These phase fluctuations are thought to be responsible for the transition to a non-superconducting state, thus even moderate cooling of this specific degree of freedom, as opposed to the entire material, may provide a novel route to stabilizing superconductivity above its critical temperature.

This theory DPhil project will work towards this grand challenge by investigating in detail the interaction between various strongly correlated electron systems and light both in and out of a cavity. Regimes of moderate and strong coupling to desired degrees of freedom, such as superconducting order parameter for stacks of Josephson junctions, will be determined. Various approaches will be pursued, such as using the cavity to perform continuous weak measurements to steer the state of the system, or strongly driving structural modes of the material to dynamically modulate its electronic properties. Combinations of phenomenological, mean-field, and numerical techniques will be applied to characterise the response of the system. Insight from these studies should lay the foundations for gauging the physical parameter space in which techniques for phase cooling are possible, and to what extent.

### 3) Quantum simulation with Rydberg atoms in optical lattices

Rydberg atoms are atoms in states of high principal quantum number that interact via the strong and very well controlled dipole-dipole (DD) interaction. The long-range nature of the DD interaction allows one to go beyond the standard regime of cold atom experiments where contact interactions prevail. In the regime of ultra-cold Rydberg atoms, the DD interaction is much larger than kinetic energies giving rise to very low effective temperatures. Systems of DD interacting Rydberg atoms are thus ideal candidates for the investigation of strongly correlated quantum systems, the simulation of condensed matter models and the development of novel quantum materials and their applications in quantum information theory.

This theory DPhil project considers Rydberg atoms in optical lattices and aims at the realization, characterisation and simulation of strongly correlated quantum systems in this setup. The project benefits from a close collaboration with Prof Wenhui Li at the Centre for Quantum Technologies (CQT) in Singapore, who is setting up an experiment with Rydberg atoms in optical lattices. The DPhil student is encouraged to engage in this collaboration. During the course of the project the candidate will become acquainted with quantum optics and quantum many body systems, and develop numerical as well as analytical skills for the description of these systems.

### 4) Quantum probes of quantum systems, impurities in cold atomic gases

Researchers in many areas have recently separately considered extracting information about a quantum system by bringing it temporarily and coherently into contact with another smaller quantum system, a probe, which is then measured. This has several advantages over traditional methods for measuring properties of a quantum system: It has the potential to be non-destructive; the potential to exploit entanglement and superposition of a perhaps spatially-extended probe in order to extract information directly about complicated correlation functions; and can involve strong interactions and thus occur on smaller time-scales than, say, linear response, and measure non-equilibrium properties. This theoretical DPhil project focuses primarily on impurity atom probes of cold atomic gases, how they could be realised, what information could be extracted or new regimes probed, and the role such probes could play in current or near-future experiments (our theory group is in contact with the experimental groups of Chris Foot, Oxford, and Stefan Kuhr, Strathclyde). Initial avenues of exploration would include using a highly-trapped impurity atom (localised to a few nm rather than the μm resolution of light) to probe a cold atomic gas on length-scales at which mean-field descriptions break down and the corpuscular nature of the gas appears, or using multiple atomic probes to identify whether number conservation occurs in the Bose-Einstein condensation of an atomic gas. This collaborative project will build upon the numerical and analytical expertise of the group in describing the evolution of impurities in cold atom systems, giving the student a firm background in these methods specifically and the vast and exciting area of cold atom physics in general.

d [dot] jaksch1 [at] physics [dot] ox [dot] ac [dot] uk |

### Dr Axel Kuhn

### 1) Bi-directional quantum interfaces between trapped atoms and light.

This project is based on three key technologies that have been 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. The combination of these three streams to a novel key technology is highly exciting as it will be one cornerstone in scaling the atomic approach to quantum computing to useful dimensions.

For further information about this project, please consult our webpage (http://www2.physics.ox.ac.uk/research/the-atom-photon-connection) and our most recent publications prior to contacting us.

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a [dot] kuhn1 [at] physics [dot] ox [dot] ac [dot] uk | 01865 272 333 |

### 2) Hybrid quantum gates and circuits in atom-photon quantum networks.

This project is aiming at the combination of integrated optics with single photons from strongly coupled atom-cavity systems. Beside demonstrating linear-optical quantum gates, multi-mode interferometers and photonic quantum walks, the major 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 to effectively extend a purely optical processing scheme with atomic quantum memories.

For further information about this project, please consult our webpage (http://www2.physics.ox.ac.uk/research/the-atom-photon-connection) and our most recent publications prior to contacting us.

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a [dot] kuhn1 [at] physics [dot] ox [dot] ac [dot] uk | 01865 272 333 |

### Dr David Lucas

### Ion Trap Quantum Computing with 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 built the best qubit in the world, using a single ion held in an ion trap. The qubit has a coherence time of 50 seconds, 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 a 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 trap to incorporate on-board microwave circuitry, and is built using a technology which is in principle scalable to much larger numbers of qubits. We are looking for a highly motivated first-class student to join this project.

Telephone | Website | |
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d [dot] lucas1 [at] physics [dot] ox [dot] ac [dot] uk | 01865 272 384 | www.physics.ox.ac.uk/users/iontrap |

### Dr Igor Mekhov

### Theoretical Quantum Optics of Ultracold Quantum Gases and Nanostructures

Both quantum optics and many-body physics of the lowest achievable temperatures are very active fields of modern research. However, the interaction between them is far from being complete. For example, in the most theoretical and experimental works on ultracold atoms, the role of light is reduced to a classical tool for preparing intriguing atomic states. In contrast, the main goal of this project is to develop a theory of the phenomena, where the quantum natures of both ultracold matter and light play equally important roles. The experiments on this ultimate quantum level of the light-matter interaction became possible just several years ago, which makes the interaction between the theory and experiment promising.

This project is focused on the development of models describing the interaction of quantum many-body systems (ultracold atoms or molecules) with quantized light. This interaction can be realised, for example, by trapping the quantum gas inside an optical cavity. In this case, the trapping potential cannot be described by a prescribed function as it is the case in most works. The potential is a quantum and dynamical variable, and the self-consistent solution for light and atomic dynamics is required. Moreover, the light can be used as a probe for the atomic state. As this is a fully quantum problem, the quantum nature of the measurement procedure has to be taken into account. In all those problems, the quantum light-matter entanglement plays a key role, allowing the application for quantum information processing, quantum simulations of condensed matter systems, and quantum metrology.

The ultimate goal of this project is to develop a theory of quantum control for strongly correlated many-body systems, which is currently unavailable. The theoretical methods to be used originate from atomic, optical and condensed matter physics. Moreover, the models developed for atoms will be applied for the solid state systems used in quantum nanophotonics (e.g. quasiparticles in semiconductor microcavities).

The candidates with interest and expertise in either Atomic, Molecular and Optical or Condensed Matter Physics are welcomed to apply. For more information, please, visit http://www2.physics.ox.ac.uk/contacts/people/mekhov

Duration: 3 years

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i [dot] mekhov1 [at] physics [dot] ox [dot] ac [dot] uk | 01865 272 330 |

### 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. These include the development of:

• 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

• New physics at the intensity frontier

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. I can offer projects in all of these areas – please contact me to discuss your interests and let’s take it from there.

Application deadline: n/a

Funding source: EPSRC DTA - tbc

Duration: 3 years

p [dot] norreys1 [at] physics [dot] ox [dot] ac [dot] uk |

### Dr Josh Nunn and Professor Ian Walmsley

### 1) D.Phil. in quantum memory and photonic applications

We invite applications from first-class students to join our group in Oxford for a D.Phil project on quantum memory, to start in 2014 (start date negotiable), supervised jointly by Joshua Nunn and Ian Walmsley.

The Ultrafast Group in Oxford has pioneered a GHz bandwidth optical memory in cesium vapour based on Raman scattering, with a world-leading time-bandwidth product exceeding 3000. Memories of this kind are a key component of future quantum technologies. The next steps in our research are to demonstrate single-photon operation, which requires engineering the density of scattering states to suppress noise and boost the memory efficiency. We are also working on an integrated memory in hollow-core optical fibre. In this project, the student will combine these ideas and develop a broadband quantum-capable integrated memory in the first two years of work. This will then be applied to the synchronisation of photon sources, or other photonic primitives, in the final year. The project is focussed on enabling the next generation of quantum photonic processors by synchronisation. The student will gain experimental skills in quantum optics, fibre optic and waveguide design, optical cavities, non-linear optics and atomic physics, as well as theoretical modelling of coherent light-matter interactions and quantum networks. There is also considerable opportunity for collaboration with other teams in the group working on integrated photonic circuits and advanced photodetection, and with other research groups both nationally (Southampton; Imperial) and internationally (Paderborn, Germany; NIST, USA), which are jointly funded.

For more details please contact Josh Nunn or Ian Walmsley:

j [dot] nunn1 [at] physics [dot] ox [dot] ac [dot] uk |

I [dot] Walmsley1 [at] physics [dot] ox [dot] ac [dot] uk |

### 2) D.Phil. in diamond photonics with NV ensembles

We invite applications from first-class students to join our group in Oxford for a D.Phil project on diamond photonics, to start in 2014 (start date negotiable), supervised jointly by Joshua Nunn and Ian Walmsley.

Quantum information processing using light offers radical new technologies such as super-fast quantum computers and super-secure quantum communication. But a key stumbling block is the ability to engineer strong light-matter interactions. These are required both to mediate photonic logic gates, and to enable the efficient storage and switching of photonic wavepackets to form a scalable architecture. Our group has developed one of the world's leading quantum memories based on Raman scattering in an atomic vapour. We are now investigating ways to integrate this memory inside a solid medium. In this project, the student will design an implementation of the memory based on the Raman interaction in an ensemble of nitrogen-vacancy (NV) defect centres in diamond, and build an experiment to demonstrate this solid state Raman memory. Looking further ahead, the same Raman interaction could be used to generate heralded, near-deterministic non-linearities at the single photon level based on Stokes scattering followed by measurement-induced quantum back-action. These research tasks are open-ended but the demonstration of a broadband light-matter interface in the solid state will be a transformative step forward in quantum photonics that will have a broad impact on the community. The student will have the opportunity to participate in active collaborations with Steven Prawer in Melbourne (fabrication) and Gerard Milburn in Brisbane (theory).

For more details please contact Josh Nunn or Ian Walmsley:

j [dot] nunn1 [at] physics [dot] ox [dot] ac [dot] uk |

I [dot] Walmsley1 [at] physics [dot] ox [dot] ac [dot] uk |

### Professor Andrew Steane

### 1) Exploring the limits of quantum coherence

This project is mainly theoretical, but will involve acquiring in-depth knowledge of at least one type of experimental method, namely trapping and cooling of charged particles ("ion trapping"). The aim of the project is to explore the idea that quantum interference has natural limits associated with the scale of the physical system. One such limit would be owing to spontaneous collapse processes that are implied by some quantum descriptions of space time. Another limit would be owing to Unruh radiation (a thermal radiation associated with accelerating through the vacuum). After these areas have been explored, it is expected that the project will develop towards understanding the possible role of quantum coherence in biological settings.

a [dot] steane1 [at] physics [dot] ox [dot] ac [dot] uk |

### Dr Brian Smith

### 1) Photonic time-frequency quantum information:

Photonic time-frequency quantum information: The first project aims to develop techniques to generate, control, and measure the time-frequency state of individual photons for quantum applications including precision measurement and computation. This will utilize photons produced via the nonlinear optical process of spontaneous parametric down conversion. By using high-speed phase modulation techniques to modify the time-frequency state, this project will explore different approaches to implement basic quantum operations, such as single particle logic operations. Different approaches to characterization of the photonic states produced such as the use of fast time-resolving detectors, precise spectral detection or hybrid measurements will be examined to optimize the information extraction.

### 2) Continuous-variable quantum information:

The second project will focus on approaches to implement quantum information primitives such as logic operations and readout for so-called continuous variable encoding, which utilizes the amplitude and phase of a single mode of the electromagnetic field. Work here will develop methods to create, process and detect quadrature-encoded quantum information. This will involve development of two-mode pulsed squeezed light sources for synchronized operations, techniques to manipulate and measure these states for quantum information applications such as the distribution of entanglement.

We are looking for self-motivated individuals who are interested in both the theoretical and experimental issues surrounding quantum information and optical quantum technologies who will contribute to these projects. For more information please contact Brian Smith.

b [dot] smith1 [at] physics [dot] ox [dot] ac [dot] uk |

### Professor Ian Walmsley and Dr Steven Kolthammer

### 1) Linear optical quantum computation

Optics provides a rich physical system to investigate how quantum mechanics opens up fundamentally new approaches to information processing. This project will investigate two important experimental aspects of optical quantum computing: (1) computational complexity as an essential feature of simple quantum optical apparatus; (2) physical requirements for universal quantum computing. Progress on these fronts will leverage state-of-the-art methods developed in the Ultrafast Quantum Optics group to generate, manipulate, and measure quantum states of light. Integrated photonic chips will be used to operate large arrays of photon sources and construct complex many-mode photonic circuits. Superconducting detectors will be used to count single photons with unsurpassed precision. On the one hand, this project strives to build limited-purpose quantum processors that provide direct evidence for the realization of quantum-enhanced computation. On the other hand, this project will achieve the first experimental demonstration of essential optical protocols for universal quantum computation and identify the primary technical obstacles to large-scale quantum computation.

The student will gain expertise in experimental quantum optics and optical quantum computation, and a thorough understanding of both the physics of optics and information. The experimental focus of the project will involve a broad range of laboratory proficiencies, from experimental design to data acquisition and analysis, and technical skills, such as using and designing integrated optical devices, cryogenic photodetectors, and ultrashort pulsed lasers. Guided by the experimental state of the art, the student will learn leading theoretical approaches to quantum information and devise laboratory tests that reveal new aspects of quantum computing. This project will engage closely with formal collaborators worldwide, including integrated optics researchers at the University of Southampton and the University of Paderborn.

For further information please contact Dr Steven Kolthammer or Professor Ian Walmsley.

i [dot] walmsley1 [at] physics [dot] ox [dot] ac [dot] uk |

s [dot] kolthammer [at] physics [dot] ox [dot] ac [dot] uk |

### Professor Ian Walmsley and Dr Steven Kolthammer

### 2) Large-scale quantum states of light distributed in time

Over the last decade, experimental quantum optics has played a pivotal role in our growing understanding of the essential features of quantum theory, from foundational principles to consequences in information theory. While optics continues to be an important platform for such studies, a key limitation concerns the scale of quantum optical systems that can be effectively manipulated. To date, work to overcome this has primarily focused on controlling quantum light in spatial mode structures of increasing complexity – for example, by building large multimode interferometers or manipulating the orbital angular momentum of light. In this project, we instead take our motivation from classical telecommunication, in which extremely high bit rates are achieved by encoding information in the time-frequency structure of light. In particular, we will develop experimental tools to manipulate the temporal structure of quantum light, which will provide access to extremely large Hilbert spaces for photonic states. Two routes will be investigated: fast nonlinear-optical or electro-optical switching will be combined with guided-wave delays, and fast polarization switching will be combined with birefringent retarders. Both methods are naturally suited to nonlinear-optical sources of quantum light driven with high repetition by ultrashort laser pulses. These new tools will then be applied to investigating unexplored quantum phenomena from multipartite entanglement to multi-particle quantum walks.

The student will gain expertise in experimental quantum optics, nonlinear optics, and integrated photonics. Alongside a thorough training in optical physics, the student will engage with on-going research in quantum theory and quantum information. While research is expected to have a strong laboratory emphasis – including experimental design, testing, and analysis – this will be balanced with a fundamental motivation to access new regimes of quantum light and understand their implications for quantum information.

For further information please contact Dr Steven Kolthammer or Professor Ian Walmsley.

i [dot] walmsley1 [at] physics [dot] ox [dot] ac [dot] uk |

s [dot] kolthammer [at] physics [dot] ox [dot] ac [dot] uk |

### Professor Ian Walmsley and Dr Steven Kolthammer

### 3) Optical quantum state engineering

Quantum physics is in an exciting period of development spurred on by new connections to information theory as well as new experimental methods to control quantum systems. In operational terms, quantum systems allow for distinct advantages over their classical counterparts for tasks including computation, communication, and measurement. A major goal for researchers is to identify the underlying physical phenomena that account for these differences. In this project, we seek to construct and analyse new quantum-mechanical states of light in the laboratory to investigate both fundamental questions about quantum theory and quantum applications in information science.

The Ultrafast Quantum Optics group at Oxford has extensive expertise in generating and measuring quantum states of light – from single photons to bright squeezed vacuum – using ultrashort pulsed lasers and nonlinear optics. We have recently developed an array of new methods employing guided-wave optics that allow access to photonic states with unprecedented scale. Nonlinear interactions in micron-scale waveguides generate multi-photon quantum states in well-controlled optical modes. Photonic chips enable complex and robust phase-stable linear optical manipulation. Superconducting photodetectors – the highest efficiency photon counters in the world – provide for precise optical measurements. The aim of this project is to characterise these new tools in a rigorous quantum-mechanical framework, and then to use them to generate, manipulate and measure novel, large-scale quantum states. Studies will investigate optical measurements that span both the wave and particle nature of light. Large multimode quantum states will allow new investigations of quantum correlation, including multipartite quantum discord and entanglement.

We are looking for a candidate with a strong interest in fundamental physics who also enjoys solving challenging technical problems. Work will be carried out as part of a large team of experimental and theoretical quantum physicists, both in Oxford and collaborating institutions worldwide. The student will gain expertise in experimental and theoretical quantum optics, as well as extensive experience with optical physics, quantum information, integrated photonics, and experimental design.

For further information please contact Dr Steve Kolthammer or Professor Ian Walmsley.

i [dot] walmsley1 [at] physics [dot] ox [dot] ac [dot] uk |

s [dot] kolthammer [at] physics [dot] ox [dot] ac [dot] uk |

### Professor Ian Walmsley and Dr Animesh Datta

### 4) Optical quantum metrology

A striking consequence of quantum theory is that fundamental limits on the information gained by a quantum-mechanical measurement apparatus can exceed that possible with a classical instrument. The field of quantum metrology seeks to identify situations in which such advantages can arise, the essential quantum resources required of the apparatus, and the approaches with which quantum-enhanced measurements can be realized in the laboratory. Despite continuing improvements in the experimental control of quantum systems, practical quantum metrology is limited due to the inherent sensitivity of quantum probes to undesired environmental disturbances. In this project, we seek to clarify the required resources for quantum-enhanced metrology and to devise new optical strategies for quantum measurements that are robust against imperfections including dephasing and dissipation.

Through both theoretical and experimental progress, we will develop approaches that impact the fundamental limitations of real laboratory measurements. Of particular interest is the simultaneous measurement of multiple parameters – quantum imaging – for which multipartite entanglement is of interest. We will study the role of probes with both fixed and indefinite photon number, as well as probes and detection methods which are both Gaussian and non-Gaussian in nature. Experiments will leverage state-of-the-art methods developed by the Ultrafast Quantum Optics group for the generation, manipulation, and detection of quantum states of light derived from ultrashort laser pulses; these studies will investigate precise optical interferometry and eventually measure real world samples.

For this challenging project, we seek a candidate with a strong interest in fundamental quantum physics, drawn to both theoretical problems and detailed experimentation. The student will gain expertise in quantum theory, the information theory of measurement, and experimental quantum optics. The project will be conducted within our team researchers studying a wide variety of quantum optics and quantum information at Oxford and will also include opportunities to work with formal collaborators in the UK and abroad.

For further information please contact Dr Animesh Datta or Professor Ian Walmsley.

i [dot] walmsley1 [at] physics [dot] ox [dot] ac [dot] uk |

a [dot] datta1 [at] physics [dot] ox [dot] ac [dot] uk |

### Professor Justin Wark

### 1) Stellar Physics with X-Ray Lasers

Stellar environments are hot and dense, leading to ionized matter at high temperatures, and with interatomic spacings sufficiently close that the bound states of a particular ion are strongly influenced by their neighbours, reducing the energy needed to ionize the atom (a phenomenon known as ionization potential depression. Similar circumstances arise in the centre of inertial confinement fusion capsules. Research within our group has recently shown that we can use the world's most powerful x-ray laser, based at SLAC California, to make solid density matter at 2 million degrees, and then probe it to find out exactly the value of the ionization potentials.

Surprisingly we found that the values were completely at odds with the standard theory that has been in wide use for over half a century.

With the aid of ab initio quantum calculations we are starting to

understand why this is the case, but much more work needs to be done.

In this project the student will be engaged in further experiments to make 'miniature stars' in the laboratory, as well as embark on fundamental quantum calculations of the properties of atoms under similar conditions to those that exist half way to the centre of the sun. The results could also have a direct impact on the quest to produce virtually limitless energy via inertial fusion techniques, and the group has strong formal links with the US National Ignition Facility.

j [dot] wark1 [at] physics [dot] ox [dot] ac [dot] uk |

### 2) Making Giant Planets in the Laboratory

New planets, far from our solar system, are being discovered on an almost daily basis. Some idea of their composition (and thus perhaps means of formation and ability to support life) can be gained simply from knowing their mass and radius - from which we can make inferences about their composition, but only if we know the compressibility of matter at ultra high pressures. For example, the centre of Jupiter has a pressure of order 70 million atmospheres. It is thus possible that 'rocky' matter can exist at ultra high pressures, but whilst we can carry out ab initio quantum calculations of its properties, up to now we have not been able to make such matter in the laboratory. In this project, the student will do just that.

By using the largest laser system in the world - the National Ignition Facility in California - we will compress solid matter, for a few nanoseconds, to pressures many times those at the centre of the earth. Some of the laser beams are used to create a laser-plasma based x-ray source, that can produce nanosecond diffraction images of the sample, allowing the probing of its structure.

j [dot] wark1 [at] physics [dot] ox [dot] ac [dot] uk |

### 3) Laboratory astrophysics with high power lasers

Topic: We plan to use high power lasers in order to study cosmic ray acceleration at supernova shocks. Using the fact that hydrodynamic equations are scale invariant, supernova shock waves can be reproduced in the laboratory using large lasers that simulate the initial blast. The project will aim at studying the dynamics of shocks in presence of magnetic fields and their role in transferring energy to charged particles. Experiments will be conducted at laser facilities in the UK as well as overseas.

j [dot] wark1 [at] physics [dot] ox [dot] ac [dot] uk |

g [dot] gregori1 [at] physics [dot] ox [dot] ac [dot] uk |

Details on these projects can be found at

https://www2.physics.ox.ac.uk/research/oxford-centre-for-high-energy-den...