Workshop Program
Thursday 17th
10.00 onwards - Registration and Coffee
11.15 - 11.30 - Welcome and introduction to the workshop
11.30 - 12.30 - 3 contributed talks (Radu Ionicioiu, Jacek Kasprzak, Brian Geradot)
12.30 - 13.00 - Invited Talk (Prof Peter Smith)
13.00 - 14.00 - Buffet Lunch
14.00 - 14.30 - Invited Talk (Dr Robert Hadfield)
14.30 - 16.30 - Poster Session and Refreshments
16.30 - 17.15 - Plenary Talk (Prof Susumu Noda)
17.15 - 19.30 - Discussion and Free Time
19.30 - 21.30 - Dinner
Friday 18th
09.00 - 10.00 - 3 contributed talks (Alex Crosse, Mark Tame, Alberto Peruzzo)
10.00 - 11.00 - Coffee Break
11.00 - 11.45 - Plenary Talk (Prof Geoff Pryde)
11.45 - 13.00 - Workshop, Discussion and Lab Tours
13.00 - 14.00 - Buffet Lunch
14.00 - 15.00 - 2 invited talks (Ian Walmsley + Terry Rudolph)
15.00 - 15.40 - Tea and Discussion
15.40 - 16.20 - 2 contributed talks (Jonathan Matthews, Xiao-Qi Zhou)
16.20 - 16.30 - Closing remarks
See below for abstracts of the talks and poster presentations:
Keynote Speakers
We are very proud to announce that there will be two keynote speakers at the workshop.
Professor Susumu Noda
"Manipulation of photons by photonic crystals - Recent Progresses and New Trends."
Prof. Susumu Noda received B.S., M.S., and Ph.D. degrees in electronics from Kyoto University, Japan, in 1982, 1984, and 1991, respectively. From 1984 to 1988, he was with Mitsubishi Electric Corporation, and was engaged in research on optoelectronic devices such as multiple quantum well distributed feedback lasers. In 1988, he joined Kyoto University, and is currently a professor of the Department of Electronic Science and Engineering. Since 2000, he has also served as Research Director of CREST, Japan Science and Technology Corporation. His research interest covers quantum optoelectronics including photonic crystals and quantum nano-structures. He has an author of more than 150 scientific journals including Nature and Science on these research subjects.
Prof. Noda is a member of IEEE, IEICE, and JAPS. He received Ando Incentive Prize, Marubun Incentive Prize, and an IBM Science Award, in 1991, 1999, and 2000, respectively.
Professor Geoff Pryde
"Noiseless linear amplification and distillation of entanglement"
Griffith University, Australia
We describe and experimentally demonstrate the idea of noiseless linear amplification of a harmonic oscillator. While deterministic amplification of this kind violates the quantum no-cloning theorem, nondeterministic heralded amplification is possible. We demonstrate an experimental circuit to realize this concept, and use it for a simple distillation of field entanglement. The concept has application to the distillation of continuous-variables EPR entanglement and quantum communications tasks.
Prof. Geoff Pryde presently heads the Quantum Optics and Information Laboratory at Griffith University (Brisbane, Australia), where he is a Senior Lecturer and Australian Research Council Centre of Excellence Research Fellow. Prior to this, he was a Senior Research Fellow in the Quantum Technology Lab at the University of Queensland and before that, a postdoc in the group of Rufus Cone at Montana State University, where he worked on the dynamics of optical pumping and FM spectroscopy, and laser stabilization to spectral holes in inpurity-ion solids. Even earlier, Geoff was a PhD student in the group of Neil Manson and Matt Sellars at the Australian National University, where he performed the precursor experiments to their present quantum information processing work.
Prof. Pryde’s research is primarily concerned with the quantum nature of things - exploring the quantum world, and understanding quantum physics to make it useful for new technologies. He is well known for work in the fields of quantum information, quantum computation, quantum communication, quantum measurement, quantum control, and coherent control of semiclassical systems.
Invited Talks
UV written waveguides for photonic quantum circuits
P.G.R. Smith, D. Kundys, J.C. Gates, C. Holmes, B.D. Snow, R.M. Parker
University of Southampton
Integrated optical circuits provide an important technology within optical telecommunications, and are also major subjects of research in optical chemical and biological sensors. Recently, however, their application in quantum information processing has attracted considerable attention within the research community, as they offer a robust and reliable route to realising experiments on a chip that would require whole optical benches of bulk optics.
This talk will provide a background to technologies for creating optical circuitry, review their existing uses within optics, will look at the elements required to achieve meaningful quantum operations, and will highlight the recent uses of laser direct write to create optical waveguides. In particular, the UV direct write approach pioneered at COM in Denmark and at the ORC in Southampton will be shown to allow the creation of low loss, fibre compatible waveguides, enables the fabrication of cross-couplers and allows ready incorporation of Bragg gratings, thermo-optic elements and liquid crystal tunable elements. Results from the application of UV written waveguides to quantum circuits will be presented.
Quantum photonics with superconducting single-photon detectors
Robert H Hadfield
Heriot-Watt University, Edinburgh, UK
Advanced optical quantum information processing applications place stringent demands on the performance of key components such as single-photon detectors. A new class of single-photon detectors based on superconducting nanowires has recently emerged, offering telecom-wavelength sensitivity, combined with low dark counts, short recovery times and low timing jitter. I will describe the basic operating principle of this type of device, the current state-of-the-art and prospects for improvements. I will also discuss implementations of these devices in quantum information processing applications such as quantum key distribution.
A photonic cluster state machine gun
Terry Rudolph
Imperial College
Cluster states are multi-qubit entangled states which have the remarkable property that, once prepared, they can be used to perform quantum computation by making only single qubit measurements. The problem of constructing a quantum computer therefore reduces to that of preparing these states. Over the last few years one of the more promising architectures for doing so has been single photon optics. However the resource requirements are still prohibitive. In this talk I will discuss a way of turning a single photon source - in particular one built from a self-assembled quantum dot - into a device capable of firing out long strings of entangled cluster state. Such a device would reduce the resource requirements for optical quantum computing by many orders of magnitude.
Elements of photonic quantum networks
Ian Walmsley
University of Oxford
The distribution and utilization of entanglement in communications, computation and metrology places strict requirements on the physical elements that generate manipulate and detect the photons carrying these correlations. I shall describe recent progress in developing and characterizing some of these elements, including pure-state photon sources based on waveguided nonlinear optics, active manipulation of quantum interference in waveguide circuits, simple broadband quantum memories and flexible photon-number resolving detectors.
Contributed Talks
Efficient preparation of 2D and 3D cluster states with photonic modules
Radu Ionicioiu
HP Labs
I describe a new photonic module which prepares, deterministically, photonic cluster
states using an atom in a cavity as an ancilla. Based on this module I discuss a network
architecture for constructing 2D cluster states and then extend the architecture to 3D topological cluster states. Advantages of this design include a passive switching mechanism and the possibility of using global control pulses for the atoms in the cavity.
Up on the Jaynes-Cummings ladder of a quantum dot-microcavity system
J. Kasprzak, S. Reitzenstein, E. A. Muljarov, C. Kistner, C. Schneider, M. Strauss, S. Höfling, A. Forchel and W. Langbein
Cardiff University
Light and matter can be unified under the strong coupling regime, yielding entities being
superpositions of both, that are oten referred as dressed states or polaritons. Strong coupling is an essential ingredient in the exciting physics spanning from many-body quantum coherence phenomena, like Bose Einstein condensation, to cavity quantum electrodynamics (cQED). A widely used approach within cQED is the Jaynes-Cummings (JC) model that describes the interaction of a single fermionic two-level system with a single photon mode. For a photon number larger than one, known as quantum strong coupling, a significant anharmonicity is predicted for the ladder-like spectrum of dressed states. For optical transitions in semiconductor nanostructures evidence of the quantum strong coupling is still missing. Here we employ coherent nonlinear spectroscopy to demonstrate quantum strong coupling in a solid state microcavity system. We measure and simulate its four-wave mixing response, granting direct access to the first two rungs of the JC ladder.
Optically Manipulating and Probing Hole-Spin in a Single Quantum Dot.
Brian D. Gerardot, Daniel Brunner, Paul A. Dalgarno, Nick G. Stoltz, Pierre M. Petroff, and Richard J. Warburton
Department of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
Materials Department, University of California, Santa Barbara, 93106, USA
A significant challenge for applications in quantum information processing is finding a highly coherent quantum state in a semiconductor. Spin is a natural choice. A single spin can be trapped in a quantum dot to isolate it from phonons, a major source of dephasing. However, an electron spin interacts with ~ 10,000 nuclear spins in a quantum dot. Unless the nuclear spins are controlled, a complex undertaking, the electron spin coherence quickly dissipates. An alternative is a hole spin in the valence band, which does not directly couple to the nuclear spins. I will present recent results which exploit quantum optical techniques to initialize, manipulate, and read-out single spins in a quantum dot embedded in a charge-tunable device. Remarkably, the hole spin is found to be highly coherent. This discovery is made by observing coherent population trapping, an optical quantum interference phenomenon, with a single hole spin.
Quantum electrodynamics in absorbing nonlinear media
J. A. Crosse, Stefan Scheel,
Quantum Optics and Laser Science, Blackett Laboratory, Imperial College London,
Prince Consort Road, London, SW7 2BW, UK.
The effects of lossless dielectric media, described by a real susceptibility, on an applied electric field have been studied at length both classically and in the framework of quantum optics. However, it can be shown that any causal response function, such as the susceptibility, is necessarily complex, with the real and imaginary parts related by the Kramer-Kronig relations. Hence absorption, which is associated with the imaginary part of the susceptibility, is an unavoidable effect in causal dielectrics. The inclusion of absorption into a quantum description of matter assisted electromagnetic fields provides a rich area for new phenomena. A quantum field theory approach to linear optics in absorbing media has been known for sometime and involves expanding the electric field in terms of the classical Green’s tensor and fundamental bosonic fields [1,2]. This approach has proved successful in describing many linear optical processes. More recently attempts have been made to extend this approach to non-linear media [3,4]. Here we present current work on the derivation of an effective Hamiltonian for the two photon nonlinear process of parametric down conversion. The resulting Hamiltonian indicates the existence of new noise field interactions which are not present in the standard descripton of onlinear optics, such as the ability for pump photons to down converting to one or no photons with the associated appearence of one or two noise field excitations respectively.
These absorptive processes have the potential to put serious limits on the ability to produce strongly correlated photon pairs for quantum information processing and quantum computational applications.
[1] Knöll L, Scheel S and Welsch D-G Coherence and Statistics of Photons and Atoms
ed. J Pe'rina (New York, Wiley, 2001) p.1
[2] S. Scheel and S. Y. Buhmann Acta Phys. Slov. 58 (2008) 675-810
[3] Scheel S and Welsch D-G Phys. Rev. Lett. 96 (2006) 073601
[4] Scheel S and Welsch D-G J. Phys. B: At. Mol. Opt. Phys. 39 (2006) S711-S724
Experimental realization of many-photon symmetric states for multiparty quantum networking
Mark Tame,
University of Belfast
Multipartite entanglement is central to studies probing the foundations of quantum physics and represents a key component in a wide range of quantum information processing tasks. So far, GHZ, W, cluster and graph states have been studied and experimentally investigated. However, many other nonequivalent classes of quantum states with interesting and unusual symmetries exist.
I will talk about a recent experiment to generate and investigate four-, five- and six-photon representatives of the important class of Dicke states. A flexible linear-optics setup will be presented where information is encoded in the polarization degrees of freedom of entangled photons produced by high-order spontaneous parametric down conversion. I will show how the generated states can be detected as genuinely multipartite entangled by using tailor-made and experimentally favorable witness tools. I will also highlight the potential for quantum control in large Hilbert spaces by discussing the evaluation of protocols such as telecloning, open-destination teleportation and quantum secret sharing.
Manipulation of photonic quantum states and a compiled quantum algorithm using Silica waveguides.
J. C. F. Matthews, A. Politi, A. Stefanov, and J. L. O’Brien
Centre for Quantum Photonics, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol, BS8 1UB, UK
Present address: Federal Office of Metrology METAS, Lindenweg 50, CH-3003, Bern-Wabern, Switzerland
Demonstration and application of two-photon quantum interference in waveguide provides a new platform for pursuing photon based quantum technologies and fundamental quantum optics [A. Politi et. al. Science 320, 646 (2008)]. We discuss a means, using resistive heating elements, to directly manipulate photonic qubits and entangled multi-photon N00N states within waveguide circuits [J. C. F. Matthews, A. Politi, A. Stefanov, J. L. O’Brien, Nat. Photon. 3 346 (2009)]. We also integrate several quantum circuits to factorize 15 on a single waveguide chip by realizing a compiled version of Shor’s quantum factoring algorithm [A. Politi, J. C. F. Matthews, J. L. O’Brien, Science, 325, 1221 (2009)].
Towards fault tolerant quantum photonic circuits
Alberto Peruzzo, Anthony Laing, Alberto Politi, Maria Rodas, Matthaeus Halder, Timothy C. Ralph, Mark G. Thompson and Jeremy L. O'Brien
Centre for Quantum Photonics, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol, BS8 1UB, UK,
Department of Physics, University of Queensland, St Lucia, Queensland 4072, Australia.
We report the first implementation of optical quantum circuits whose performance exceeds that required for fault tolerant operation. Despite impressive progress towards the realization of a quantum computer, there remain large gaps between the performance demonstrated and that required for fault-tolerant operation. Quantum computers are inherently analogue and therefore unable to benefit from the digital ‘latching’ that makes conventional computers so robust. Furthermore the quantum states in which information is encoded are inherently fragile. Nevertheless, if gates can be made to operate below stringent error-per-gate thresholds, full-scale quantum computing will be possible. We report breaking through this fault tolerance barrier for one of the leading approaches to quantum computing — the integrated photonic architecture [Science 320, 646, 2008], which we have very recently used to demonstrate a small-scale quantum factoring algorithm [Science 325, 1221, 2009]. This level of performance has previously only been seen in ion trap architectures.
A novel approach to realize quantum gates by accessing higher dimensional Hilbert space
Xiao-Qi Zhou, Timothy C. Ralph, Pruet Kalasuwan, Mian Zhang, and Jeremy L. O’Brien
Centre for Quantum Photonics, University of Bristol, BS8 1UB, United Kingdom
Department of Physics and Centre for Quantum Computer Technology, University of Queensland, Brisbane 4072, Australia
In theory, single-qubit gates and controlled-NOT(CNOT) gates already constitute a universal set of quantum gates. In practice, however, even small quantum circuits require a large number of such gates, hindering the realization of practical quantum circuitry with current technology. Here we present a novel approach to implement quantum gates by accessing higher-dimensions of Hilbert space. Instead of decomposing the quantum circuits into the elemental gates and then implementing them step by step, we directly construct the matrix of the quantum gates. This is in principle a far more intuitive, efficient and resource-saving method in a broad range of cases. To prove our theory, we realized a series of two-qubit quantum gates which include CNOT gate, CU gate, entanglement filter and entanglement splitter by using this method.
Poster Presentations
Long Range Entanglement by Bond Quenching in Spin Chain Kondo Model
Abolfazl Bayat
University College London
We show that, in the gapless Kondo regime, a single local quench at one end of a Kondo spin chain induces a fast and long lived oscillatory dynamics. This quickly establishes a high quality entanglement between the spins at the opposite ends of the chain. This entanglement is mediated by a Kondo cloud, attains a constant high value independent of the length for large chains, and shows thermal robustness. In the gapped dimmer regime of the chain, finite size end to end effects can create some entanglement on a much longer time-scale. By decoupling one end of the chain during dynamics one can distinguish between this end-end effect which vanishes, and the global Kondo cloud mediated entanglement, which persists. This quench approach paves the way to detect the elusive Kondo cloud through the entanglement between two individual spins. Our results show that non-perturbative cooperative phenomena from condensed matter may be exploited for quantum information.
Increasing the photon collection efficiency from N-V defects in diamond
A. C. Stanley-Clarke
University of Bristol
The nitrogen-vacancy (N-V) defect in diamond is a promising candidate for both solid state and linear optical quantum computation and information. It has been demonstrated as a stable single photon source at room temperature. The system can be easily initialised into the triplet ground state by optical pumping and has a very long decoherence lifetime. The spin state can be read out by examining the photoluminescence intensity. However, due to low confocal microscope collection efficiencies, single shot measurements are unable to be performed within the decoherence lifetime of the N-V spin.
Coupling of photons out of diamond to increase this efficiency can be achieved by the use of a solid immersion lens (SIL). This comprises of a hemispherical diamond lens placed directly above the defect. It can be shown by Finite Difference Time Domain simulations that the collection efficiency can be increased by a factor of 6 when SIL technology is employed. We have begun fabricating SIL structures using focussed ion beam milling techniques. This provides an integrated optics system with no interface between the lens and bulk diamond. By cutting a series of rings at increasing depths and increasing diameters the profile of a hemisphere can be approximated. Single N-V defects can be located using a scanning confocal microscope. SILs are fabricated in the correct location by the use of markers. Again, using the confocal microscope, the N-V defects will be characterised in anti-bunching experiments and measuring collection efficiency.
Coupled-cavity quantum electrodynamics
G. Lepert, M. Trupke, M.J. Hartmann, M.B. Plenio, E.A. Hinds
Imperial College, London
Recent advances in cavity quantum electrodynamics (QED) have been made possible by the development of micron-scale high-finesse cavities [1], and have opened the road to the experimental realization of the next stage of cavity QED: the interconnection of multiple atom-cavity systems. A growing body of theoretical work documents the possibilities offered by such devices [2]. It may for example be possible to study many-body quantum phenomena, which hitherto belonged to the realm of condensed matter physics, in such an array of cavities.
In this poster we present our theoretical studies towards a possible experimental realisation of such a system. The device will consist of a linear array of cavities, each made of a spherical mirror etched on silicon and a waveguide chip with reflection-coated facets. The mirror and a chip facet will be used to form a free-space optical cavity, containing atoms. Photons can tunnel from this cavity to a waveguide cavity on the chip. Waveguides are connected by tunable evanescent couplers, thus enabling controlled inter-cavity coupling. We detail in this poster the proposed device and possible experiments.
References:
[1] Trupke et al, PRL 99, 063601 (2007)>
[2] Hartmann et al, Laser & Photon. Rev. 2, No. 6, 527-556 (2008)>
Fibre source of intrinsically time bandwidth limited photon pairs
A.S. Clark, J. Fulconis, M. Halder, B. Cemlyn, J.L. O’Brien, C. Xiong, W.J. Wadsworth and J.G. Rarity
University of Bristol
University of Bath
We investigate a new phase matching scheme for pure state photon pair generation in birefringent photonic crystal fibres. We take a photonic crystal fibre (PCF) with a 2 micron solid silica core surrounded by an air hole cladding which has birefringence introduced during manufacture by modification of two of the holes adjacent to the core. We then see a modification of the phase matching to include cross-polar cases where two pump photons launched on one axis generate photons widely spaced in wavelength on the orthogonal axis.
There is an area of the modified phase matching curves which show the wavelength of the signal photon to be independent of the pump wavelength, allowing the creation of intrinsically narrowband photons around 0.13 nm in bandwidth with no spectral filtering used. We demonstrate 80% visibility non-classical interference between these unfiltered photons coming from the non-degenerate pairs and created in separate PCF sources. Using a Sagnac loop configuration of the PCF we also demonstrate high visibility fringes in non-orthogonal bases signifying entanglement between the generated photons.
Optical-Waveguide Chip for Atomic Detection
M. Kohnen, R.A. Nyman, P.G. Petrov, M. Succo, M. Trupke and E.A. Hinds
Imperial College, London
New technologies for micro-fabricating optical structures rapidly expand the possibilities of using optical circuit chips in engineering and science [1]. Applying optical chips to atom-optical experiments, a large mode-overlap between atoms and light can easily be achieved. This coupling makes local, quasi-non-demolition density measurements of cold atomic clouds and condensates possible. Such a setup might find its first application in a feedback loop on a condensate. Furthermore, optical-waveguide chips finally make atomic traps as a whole scalable, and therefore open the door for the implementation of such traps in complex quantum information processing experiments.
Our group reports on the first successful integration of such a chip in an atom-optical experiment. Our chip contains twelve waveguides, intercepted by a trench. The trench enables us to bring atomic samples into the waveguide modes and observe the interaction of the light from the waveguide with the atoms. We were able to achieve atomic densities of up to 4x10
15 m
-3 in the trench and to characterise the waveguide modes by observing the influence of the atom-photon interaction on the output light as a function of the input light’s intensity, frequency and polarisation.
[1] A. Politi, J.C.F. Matthews, and J.L. O'Brien, Since 325,1221 (2009)
Diamond microstructures for use in high Q Fabry Perot cavities
B R Patton, F Grazioso, P Dolan, and J M Smith
Department of Materials, University of Oxford, UK
B Fairchild, P Olivero, S Rubanov, A Greentree and S Prawer.
School of Physics , University of Melbourne, Australia
E Gu, Y F Zhang, C L Lee and M D Dawson
nstitute of Photonics, University of Strathclyde, UK
Colour centres in diamond are attractive in many respects for quantum information technologies. Single centres show stable single photon emission even at room temperature, and are the basis for the first commercialised 'single photon source' (www.qcvictoria.com). The remarkable coherence of electronic and nuclear spin states, and the capability to interact with these spins optically, presents possibilities for using measurement-based entanglement methods to generate large scale cluster states that can ultimately become a resource for universal quantum computing. The main technological bottleneck to producing advanced colour centre-based devices is the need to exercise control over the interaction between the electric dipole transition of the colour centre and the optical mode(s) into which it couples. The only practical way of doing so is by the construction of a high quality, small mode volume optical cavity; and for this it is necessary to fabricate microstructures in the diamond which have well understood – and preferably engineerable - optical and materials properties.
Our approach to this problem is to fabricate thin films of diamond for incorporation in to tunable, high Q Fabry Perot microcavities. We aim to achieve mode volumes of less than 50λ
3 and Q factors ~ 10
4, sufficient to give a strong Purcell effect in the ‘weak coupling’ regime. Here we will report our progress to date and comment on the challenges that remain to be met in realising the goal of efficient colour centre – cavity coupling.
