Research projects for 2013

A Laser-Cooled Single Ion Optical Clock

Dr Patrick Baird and Dr Patrick Gill, NPL

The NPL has 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 ²S_1/2 – ²F_7/2 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: ²S_1/2 – ²D_3/2) 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.

Please click here for further details.

The project offers the possibility of 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.

The project offers the possibility of funding through an EPSRC CASE award.
In the first instance, please contact: Dr Patrick Baird.

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 18th
Funding source: STFC studentship for eligible students
Duration: 3 years

Novel spectroscopy using quantum cascade lasers

The research project is part of an overall programme developing advanced optical sensors for a range of applications from basic physics to chemical, medical and environmental measurement. In particular the project aims to develop state-of-the-art quantum cascade lasers and other advanced light sources for detection of gas phase molecules in the mid-infrared spectral region. A novel spectroscopic method pioneered in our group, Multi-mode absorption spectroscopy, MUMAS, is being developed using these new light sources for ultra-sensitive detection of molecules important in environmental, medical and industrial applications. The project will suit physics or chemistry graduates with good experimental, analytical and computational skills who is interested in exploring new ideas. The research is being conducted in association with several industrial enterprises involved in gas sensing.

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

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.

Quasi-phase-matched high-harmonic generation for coherent diffractive imaging

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. Our group has developed several techniques for QPM and demonstrated that these methods can increase the energy in the harmonic beam.

In this project we will investigate new techniques for QPM and apply the bright harmonics they generate to coherent diffractive imaging (CDI). This method images objects without additional optics (which are not available at these wavelengths); it does so by recording the intensity diffraction pattern of the object and using sophisticated phase-retrieval algorithms to overcome the "phase-retrieval problem" in recreating the object.

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

Application deadline: n/a
Funding source: To be confirmed
Duration: 3 years

Plasma accelerators

In a laser-driven plasma accelerator an intense laser pulse excites a trailing plasma wave known as a "wakefield." The electric fields formed within this wave can reach 1000 times those used in conventional accelerators, thereby offering a route to very compact accelerators.
Our work on laser-driven plasma accelerators is in three areas: (i) investigation of techniques for controlling the injection of electrons into the plasma wakefield; (ii) development of techniques for staging plasma accelerators, with a view to reaching beam energies beyond 1 GeV; (iii) development of applications of laser-driven plasma accelerators, particularly their application to the generation of x-rays. We pursue these goals by both experiment and numerical modelling. We would be particularly interested in taking on a graduate student to work on the generation of radiation from laser-accelerated electron beams, although we would consider applications to work in areas (i) and (ii).

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

Application deadline: n/a
Funding source: To be confirmed
Duration: 3 years

1) Development and implementation of photon-mediated quantum gates and bi-directional quantum interfaces between individual trapped atoms.

This project is based on three key technologies that have been developed 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 techniques is a challenging task, which is highly exciting even if only partially accomplished, as it might demonstrate the scalability of the atomic approach to quantum computing.

2) Investigate the coupling of two atom-cavity systems, and realise probabilistic photonic quantum gates and circuits.

This project is footing on a recently started collaboration with the University of Bristol, which 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 ideas of this new project are 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 these projects, you may want to consult our webpage (http://www2.physics.ox.ac.uk/research/the-atom-photon-connection) and follow the links to our most recent publications prior to contacting us.

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.

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

Application deadline: n/a
Project Reference:
Funding source: EPSRC*
Duration: 3 years

*Please note: Overseas fees are not included in this funding.

Integrated Experiments for Fast Ignition Target Physics Validation

Recent advances in laser performance, experimental capability, target design, and modelling tools now provide an unprecedented opportunity for testing sub-ignition-scale cone-in-shell fast-ignition targets and validating large-scale integrated target computer simulations. The spatial distribution of fast electrons in the imploded high-density plasma core can be characterized for the first time in integrated cone-guided Fast Ignition (FI) experiments using the OMEGA beams for fuel assembly, and the high intensity EP beam focused on the cone tip for heating. In addition, new ideas and insights into mitigating the effects of electron divergence to understand and improve core-heating efficiency will be explored. The student will be expected to participate in experiment design, data acquisition and analysis using the Vulcan petawatt laser facility at the Rutherford Appleton Laboratory as well as the OMEGA laser facility in the University of Rochester. Travel to major US laser facilities in California and New York will be expected.

Application deadline: n/a
Funding source: EPSRC DTA - tbc
Duration: 3 years

Integrated Quantum Memories

Quantum information processing using light offers radical new technologies such as super-fast quantum computers and super-secure quantum communication. But a key component is required: a quantum memory that can store and release photons. 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 an optical fibre, or in a solid medium. In this project, the student will begin by pushing forward on the fibre-based memory in collaboration with a senior team member. At the same time, the student will design an implementation of the memory based on NV-centres in diamond, and build an experiment to demonstrate this solid state Raman memory. These research tasks are open-ended but the demonstration of a functional integrated quantum memory will be a transformative step forward in quantum photonics that will have a broad impact on the community. This is therefore a challenging and intriguing project that demands an excellent student, willing to engage with both theoretical and experimental details.

For more details please contact Steve Kolthammer or Josh Nunn:

Memory-enhanced Photonic Simulations

Many interesting phenomena in physics cannot be analysed because they are both quantum mechanical, and complex. Light harvesting mechanisms in photosynthesis, high-temperature superconductors and quark-gluon interactions all fall into this category of multi-particle quantum systems that cannot be simulated on any non-quantum machine. In this project the student will build a quantum simulator designed to mimic coherent energy transfer across a network. The idea is to build a number of quantum memories (devices to store photons)and to link them so that photons can be made to hop between the memories, which become the nodes of a programmable quantum network. Atomic quantum memories are themselves the subject of research and development in our group, and so the student will work closely with the existing memories team. This is a challenging project lying at the intersection of quantum optics, atomic physics, quantum information theory and the exploding field of quantum coherence in biology, and may stimulate the design of novel quantum devices. We invite applications from first-class students to take this research forward.

For more details please contact Xian-Min Jin or Josh Nunn: