Publications


Optimal experiment design for minimal tomography

Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)

J Nunn, BJ Smith, G Puentes, JS Lundeen, IA Walmsley

Given an experimental set-up and a fixed number of measurements, how should one take data in order to optimally reconstruct the state of a quantum system? We show how to calculate the optimal design explicitly. © 2010 Optical Society of America.


Complete characterization of weak-homodyne photon-number-resolving detectors: Applications to non-classical photonic state reconstructions

Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)

HB Coldenstrodt-Ronge, G Puentes, O Cohen, F Noriega, X Yang, JS Lundeen, BJ Smith, IA Walmsley

A novel detector combining phase sensitivity and photon-number resolution is experimentally characterized by measuring its positive-operator-value measurement set. Direct application to tomographic reconstruction of heralded single-photon states is presented. ©2010 Optical Society of America.


Phase-controlled photonic quantum circuits in laser written integrated optics

Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)

N Thomas-Peter, BJ Smith, D Kundys, PGR Smith, IA Walmsley

We present a direct UV-written integrated photonic circuit with on-chip phase control through a thermo-optic phase shifter. An arbitrary beam splitter and a two-photon NOON state are demonstrated with high visibility interference. © 2010 Optical Society of America.


Coherent optical memory with GHz bandwidth

Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)

KF Reim, J Nunn, VO Lorenz, BJ Sussman, KC Lee, NK Langford, D Jaksch, IA Walmsley

We demonstrate the coherent storage and retrieval of sub-nanosecond low-intensity light pulses with spectral bandwidths exceeding 1 GHz in cesium vapor, using the novel, far offresonant two-photon Raman memory protocol. © 2010 Optical Society of America.


Quantum memory in an optical lattice

Physical Review A - Atomic, Molecular, and Optical Physics 82 (2010)

J Nunn, U Dorner, P Michelberger, KF Reim, KC Lee, NK Langford, IA Walmsley, D Jaksch

Arrays of atoms trapped in optical lattices are appealing as storage media for photons, since motional dephasing of the atoms is eliminated. The regular lattice is also associated with band structure in the dispersion experienced by incident photons. Here we study the influence of this band structure on the efficiency of quantum memories based on electromagnetically induced transparency (EIT) and on Raman absorption. We observe a number of interesting effects, such as both reduced and superluminal group velocities, enhanced atom-photon coupling, and anomalous transmission. These effects are ultimately deleterious to the memory efficiency, but they are easily avoided by tuning the optical fields away from the band edges. © 2010 The American Physical Society.


Applications of Raman scattering in quantum technologies

AIP Conference Proceedings 1267 (2010) 37-38

KF Reim, P Bustard, KC Lee, J Nunn, VO Lorenz, BJ Sussman, NK Langford, D Jaksch, IA Walmsley


Nonclassical photon streams using rephased amplified spontaneous emission

PHYSICAL REVIEW A 81 (2010) ARTN 012301

PM Ledingham, WR Naylor, JJ Longdell, SE Beavan, MJ Sellars


Experimental quantum-enhanced estimation of a lossy phase shift

NATURE PHOTONICS 4 (2010) 357-360

M Kacprowicz, R Demkowicz-Dobrzanski, W Wasilewski, K Banaszek, IA Walmsley


Design of bright, fiber-coupled and fully factorable photon pair sources

NEW JOURNAL OF PHYSICS 12 (2010) ARTN 093027

L Edgar Vicent, AB U'Ren, R Rangarajan, CI Osorio, JP Torres, L Zhang, IA Walmsley


Entanglement quantification from incomplete measurements: Applications using photon-number-resolving weak homodyne detectors

New Journal of Physics 12 (2010)

G Puentes, A Datta, A Feito, J Eisert, MB Plenio, IA Walmsley

The certificate of success for a number of important quantum information processing protocols, such as entanglement distillation, is based on the difference in the entanglement content of the system quantum states before and after the protocol. In such cases, effective bounds need to be placed on the entanglement of non-local states consistent with statistics obtained from local measurements. In this paper, we study numerically the ability of a hybrid homodyne detector that combines phase sensitivity and photon-number resolution to set accurate bounds on the entanglement content of two-mode quadrature squeezed states without the need for full state tomography. We show that it is possible to set tight lower bounds on the entanglement of a family of two-mode degaussified states using only a few measurements. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Towards high-speed optical quantum memories

Nature Photonics 4 (2010) 218-221

KF Reim, J Nunn, VO Lorenz, BJ Sussman, KC Lee, NK Langford, D Jaksch, IA Walmsley

Quantum memories, capable of controllably storing and releasing a photon, are a crucial component for quantum computers1 and quantum communications2. To date, quantum memories3-6 have operated with bandwidths that limit data rates to megahertz. Here we report the coherent storage and retrieval of sub-nanosecond low-intensity light pulses with spectral bandwidths exceeding 1GHz in caesium vapour. The novel memory interaction takes place through a far off-resonant two-photon transition in which the memory bandwidth is dynamically generated by a strong control field7,8. This should allow data rates more than 100 times greater than those of existing quantum memories. The memory works with a total efficiency of 15%, and its coherence is demonstrated through direct interference of the stored and retrieved pulses. Coherence times in hot atomic vapours are on the order of microseconds, the expected storage time limit for this memory. © 2010 Macmillan Publishers Limited. All rights reserved.


All-electrical coherent control of the exciton states in a single quantum dot

PHYSICAL REVIEW B 82 (2010) ARTN 241301

AB de la Giroday, AJ Bennett, MA Pooley, RM Stevenson, N Skoeld, RB Patel, I Farrer, DA Ritchie, AJ Shields


Electric-field-induced coherent coupling of the exciton states in a single quantum dot

NATURE PHYSICS 6 (2010) 947-950

AJ Bennett, MA Pooley, RM Stevenson, MB Ward, RB Patel, AB de la Giroday, N Skoeld, I Farrer, CA Nicoll, DA Ritchie, AJ Shields


COMPONENTS FOR MULTI-PHOTON NON-CLASSICAL STATE PREPARATION AND MEASUREMENT

LASER SPECTROSCOPY (2010) 148-157

G Puentes, L Zhang, H Coldenstrodt-Ronge, O Cohen, BJ Smith, N Thomas-Peter, IA Walmsley


Two-photon interference of the emission from electrically tunable remote quantum dots

NATURE PHOTONICS 4 (2010) 632-635

RB Patel, AJ Bennett, I Farrer, CA Nicoll, DA Ritchie, AJ Shields


Giant Stark effect in the emission of single semiconductor quantum dots

APPLIED PHYSICS LETTERS 97 (2010) ARTN 031104

AJ Bennett, RB Patel, J Skiba-Szymanska, CA Nicoll, I Farrer, DA Ritchie, AJ Shields


Quantum interference of electrically generated single photons from a quantum dot.

Nanotechnology 21 (2010) 274011-

RB Patel, AJ Bennett, K Cooper, P Atkinson, CA Nicoll, DA Ritchie, AJ Shields

Quantum interference lies at the foundation of many protocols for scalable quantum computing and communication with linear optics. To observe these effects the light source must emit photons that are indistinguishable. From a technological standpoint, it would be beneficial to have electrical control over the emission. Here we report of an electrically driven single-photon source emitting indistinguishable photons. The device consists of a layer of InAs quantum dots embedded in the intrinsic region of a p-i-n diode. Indistinguishability of consecutive photons is tested in a two-photon interference experiment under two modes of operation, continuous and pulsed current injection. We also present a complete theory based on the interference of photons with a Lorentzian spectrum which we compare to both our continuous wave and pulsed experiments. In the former case, a visibility was measured limited only by the timing resolution of our detection system. In the case of pulsed injection, we employ a two-pulse voltage sequence which suppresses multi-photon emission and allows us to carry out temporal filtering of photons which have undergone dephasing. The characteristic Hong-Ou-Mandel 'dip' is measured, resulting in a visibility of 64 +/- 4%.


Slow-light-enhanced single quantum dot emission in a unidirectional photonic crystal waveguide

APPLIED PHYSICS LETTERS 96 (2010) ARTN 031109

SJ Dewhurst, D Granados, DJP Ellis, AJ Bennett, RB Patel, I Farrer, D Anderson, GAC Jones, DA Ritchie, AJ Shields


Resolution of the relative phase ambiguity in spectral shearing interferometry of ultrashort pulses.

Opt Lett 35 (2010) 1971-1973

DR Austin, T Witting, IA Walmsley

We show that multiple-shear spectral shearing interferometry can overcome the relative phase ambiguity of disjoint spectral components that is present in single-shear approaches. By upconverting the unknown pulse with spatially chirped ancillae, we achieve a shear-to-space mapping that can be acquired on an imaging spectrometer. A subset of this continuous range of shears can be chosen for robust and accurate phase retrieval using a multiple-shear algorithm.


Comparing phonon dephasing lifetimes in diamond using Transient Coherent Ultrafast Phonon Spectroscopy

Diamond and Related Materials 19 (2010) 1289-1295

KC Lee, BJ Sussman, J Nunn, VO Lorenz, K Reim, D Jaksch, IA Walmsley, P Spizzirri, S Prawer

Transient Coherent Ultrafast Phonon Spectroscopy (TCUPS) is utilized to study phonon dephasing lifetimes in various diamond types. Samples of natural, chemical vapour deposited, and high pressure high temperature diamond are compared showing significant differences. Dephasing mechanisms are discussed. © 2010 Elsevier B.V. All rights reserved.

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