Publications


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.


Amplification of impulsively excited molecular rotational coherence.

Phys Rev Lett 104 (2010) 193902-

PJ Bustard, BJ Sussman, IA Walmsley

We propose a scheme for preparation of high-coherence molecular dynamics which are phase stable with respect to ultrashort pulses. We experimentally demonstrate an example of this scheme using a phase-independent, nanosecond-duration, pump pulse to prepare a rotational coherence in molecular hydrogen. This rotational coherence is made phase stable with respect to a separate source of ultrashort pulses by seeding. The coherence is used to generate spectral broadening of femtosecond probe radiation by molecular phase modulation.


Optimal experiment design for quantum state tomography: Fair, precise, and minimal tomography

Physical Review A - Atomic, Molecular, and Optical Physics 81 (2010)

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

Given an experimental setup and a fixed number of measurements, how should one take data to optimally reconstruct the state of a quantum system? The problem of optimal experiment design (OED) for quantum state tomography was first broached by Kosut. Here we provide efficient numerical algorithms for finding the optimal design, and analytic results for the case of 'minimal tomography'. We also introduce the average OED, which is independent of the state to be reconstructed, and the optimal design for tomography (ODT), which minimizes tomographic bias. Monte Carlo simulations confirm the utility of our results for qubits. Finally, we adapt our approach to deal with constrained techniques such as maximum-likelihood estimation. We find that these are less amenable to optimization than cruder reconstruction methods, such as linear inversion. © 2010 The American Physical Society.


Quantum memories

EUROPEAN PHYSICAL JOURNAL D 58 (2010) 1-22

C Simon, M Afzelius, J Appel, AB de la Giroday, SJ Dewhurst, N Gisin, CY Hu, F Jelezko, S Kroll, JH Muller, J Nunn, ES Polzik, JG Rarity, H De Riedmatten, W Rosenfeld, AJ Shields, N Skoeld, RM Stevenson, R Thew, IA Walmsley, MC Weber, H Weinfurter, J Wrachtrup, RJ Young


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


Coherent optical ultrasound detection with rare-earth ion dopants.

Applied optics 49 (2010) 4331-4334

JW Tay, PM Ledingham, JJ Longdell

We describe theoretical and experimental demonstration for optical detection of ultrasound using a spectral hole engraved in cryogenically cooled rare-earth ion-doped solids. Our method utilizes the dispersion effects due to the spectral hole to perform phase-to-amplitude modulation conversion. Like previous approaches using spectral holes, it has the advantage of detection with large étendue. The method also has the benefit that high sensitivity can be obtained with moderate absorption contrast for the spectral holes.


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


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.


A pump-probe study of the photoassociation of cold rubidium molecules.

Faraday Discuss 142 (2009) 403-413

J Petrovic, D McCabe, D England, H Martay, M Friedman, A Dicks, E Dimova, I Walmsley

The dynamics of the excited state during the photoassociation of cold molecules from cold rubidium atoms is studied in a series of pump-probe experiments. Dipole transitions similar to those of the atoms are observed in the molecular signal. While such behaviour is characteristic of the long-range molecules, the photoassociation of bound molecules is confirmed in additional experiments. The pump-probe signal observed on a 250 ps time scale did not, however, reveal wavepacket oscillations predicted by theory. This result is discussed using numerical simulations of photoassociation and a modification to the current experiments that could lead to the detection of wavepacket dynamics is suggested.


Phase-controlled integrated photonic quantum circuits

Optics Express 17 (2009) 13516-13516

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


Study of quantum-path interferences in the high harmonic generation process

Springer Berlin Heidelberg 92 (2009) 27-29-27-29

A Zaïr, M Holler, F Schapper, L Gallmann, A Wyatt, A Monmayrant, T Auguste, J Pascal-Caumes, I Walmsley, E Cormier, P Salièeres, U Keller

High Harmonic generation can be used as a probe of the emitting medium with attosecond and Angström resolutions. We show that polarization-resolved pump-probe spectroscopy with high harmonics improves the detection sensitivity of rotationally excited molecules.

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