Publications


Large-alphabet time-frequency entangled quantum key distribution by means of time-to-frequency conversion.

Opt Express 21 (2013) 15959-15973

J Nunn, LJ Wright, C Söller, L Zhang, IA Walmsley, BJ Smith

We introduce a novel time-frequency quantum key distribution (TFQKD) scheme based on photon pairs entangled in these two conjugate degrees of freedom. The scheme uses spectral detection and phase modulation to enable measurements in the temporal basis by means of time-to-frequency conversion. This allows large-alphabet encoding to be implemented with realistic components. A general security analysis for TFQKD with binned measurements reveals a close connection with finite-dimensional QKD protocols and enables analysis of the effects of dark counts on the secure key size.


Measuring nonlocal coherence with weak-field homodyne detection

2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE AND INTERNATIONAL QUANTUM ELECTRONICS CONFERENCE (CLEO EUROPE/IQEC) (2013)

TJ Bartley, G Donati, X-M Jin, A Datta, M Barbieri, IA Walmsley, IEEE


Attosecond Sampling of Arbitrary Optical Waveforms

2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE AND INTERNATIONAL QUANTUM ELECTRONICS CONFERENCE (CLEO EUROPE/IQEC) (2013)

AS Wyatt, T Witting, A Schiavi, D Fabris, JP Marangos, JWG Tisch, IA Walmsley, IEEE


Entang-bling: Observing quantum correlations in room-temperature solids

Journal of Physics: Conference Series 442 (2013)

IA Walmsley, KC Lee, M Sprague, B Sussman, J Nunn, N Langford, XM Jin, T Champion, P Michelberger, K Reim, D England, D Jaksch

Quantum entanglement in the motion of macroscopic solid bodies has implications both for quantum technologies and foundational studies of the boundary between the quantum and classical worlds. Entanglement is usually fragile in room-temperature solids, owing to strong interactions both internally and with the noisy environment. We generated motional entanglement between vibrational states of two spatially separated, millimeter-sized diamonds at room temperature. By measuring strong nonclassical correlations between Raman-scattered photons, we showed that the quantum state of the diamonds has positive concurrence with 98% probability. Our results show that entanglement can persist in the classical context of moving macroscopic solids in ambient conditions. © Published under licence by IOP Publishing Ltd.


Heralded generation of single photons in pure quantum states

Journal of Modern Optics 59 (2012) 1525-1537

L Zhang, C Söller, O Cohen, BJ Smith, IA Walmsley

Sources of single photons in pure quantum states are essential to many quantum optics applications. We explore a technique, known as group-velocity matching, that enables the heralded generation of pure single photons through nonlinear optical processes. It reduces or eliminates the requirement of spectral filtering that conventional sources rely on to achieve high purity, therefore increasing both heralding efficiency and photon flux. Implementation in both spontaneous parametric downconversion and spontaneous four-wave mixing is studied as we discuss several recent experimental realizations demonstrating purity of more than 0.84 for the heralded photons. © 2012 Copyright Taylor and Francis Group, LLC.


Invited Review Article: Technology for Attosecond Science

REVIEW OF SCIENTIFIC INSTRUMENTS 83 (2012) ARTN 071101

F Frank, C Arrell, T Witting, WA Okell, J McKenna, JS Robinson, CA Haworth, D Austin, H Teng, IA Walmsley, JP Marangos, JWG Tisch


Characterization of the femtosecond speckle field of a multiply scattering medium via spatio-spectral interferometry

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 29 (2012) 1146-1151

A Tajalli, DJ McCabe, DR Austin, IA Walmsley, B Chatel


Continuous phase stabilization and active interferometer control using two modes

JOURNAL OF MODERN OPTICS 59 (2012) 42-45

G Jotzu, TJ Bartley, HB Coldenstrodt-Ronge, BJ Smith, IA Walmsley


Entangbling - quantum correlations in diamond

2012 IEEE PHOTONICS CONFERENCE (IPC) (2012) 410-410

IA Walmsley, IEEE


Adaptive slit beam shaping for direct laser written waveguides.

Opt Lett 37 (2012) 470-472

PS Salter, A Jesacher, JB Spring, BJ Metcalf, N Thomas-Peter, RD Simmonds, NK Langford, IA Walmsley, MJ Booth

We demonstrate an improved method for fabricating optical waveguides in bulk materials by means of femtosecond laser writing. We use an LC spatial light modulator (SLM) to shape the beam focus by generating adaptive slit illumination in the pupil of the objective lens. A diffraction grating is applied in a strip across the SLM to simulate a slit, with the first diffracted order mapped onto the pupil plane of the objective lens while the zeroth order is blocked. This technique enables real-time control of the beam-shaping parameters during writing, facilitating the fabrication of more complicated structures than is possible using nonadaptive methods. Waveguides are demonstrated in fused silica with a coupling loss to single-mode fibers in the range of 0.2 to 0.5 dB and propagation loss <0.4 dB/cm.


Turning classical states quantum with linear optics and photon counting

2012 Conference on Lasers and Electro-Optics, CLEO 2012 (2012)

TJ Bartley, G Donati, XM Jin, JB Spring, M Barbieri, BJ Smith, A Datta, L Zhang, IA Walmsley

We demonstrate a method to transmute classical light into a quantum state without invoking any nonlinear optical processes. Using a tunable beam splitter and photon number resolving measurement, we create a novel non-Gaussian state. © 2012 OSA.


Synchronizing single photons with quantum memories

2012 Conference on Lasers and Electro-Optics, CLEO 2012 (2012)

J Nunn, NK Langford, T Champion, MR Sprague, PS Michelberger, KC Lee, XM Jin, D England, WS Kolthammer, IA Walmsley

Without deterministic single photon sources, multiphoton rates fall exponentially with the number of photons required, making practical photonics unfeasible. We show how quantum memories improve multiphoton rates by many orders of magnitude. © 2012 OSA.


Generalized multishearing interferometry for the complete multidimensional characterization of optical beams and ultrashort pulses

2012 Conference on Lasers and Electro-Optics, CLEO 2012 (2012)

AS Wyatt, J Biegert, IA Walmsley

We demonstrate increased accuracy and precision in the reconstruction of the multidimensional phase of electromagnetic fields based on multiple spectral shearing interferometry measurements made with shears of an arbitrary magnitude. © 2012 OSA.


Multipulse Addressing of a Raman Quantum Memory: Configurable Beam Splitting and Efficient Readout

PHYSICAL REVIEW LETTERS 108 (2012) ARTN 263602

KF Reim, J Nunn, X-M Jin, PS Michelberger, TFM Champion, DG England, KC Lee, WS Kolthammer, NK Langford, IA Walmsley


Quantum storage of a photonic polarization qubit in a solid.

Physical review letters 108 (2012) 190504-

M Gündoğan, PM Ledingham, A Almasi, M Cristiani, H de Riedmatten

We report on the quantum storage and retrieval of photonic polarization quantum bits onto and out of a solid state storage device. The qubits are implemented with weak coherent states at the single photon level, and are stored for a predetermined time of 500 ns in a praseodymium doped crystal with a storage and retrieval efficiency of 10%, using the atomic frequency comb scheme. We characterize the storage by using quantum state tomography, and find that the average conditional fidelity of the retrieved qubits exceeds 95% for a mean photon number μ=0.4. This is significantly higher than a classical benchmark, taking into account the poissonian statistics and finite memory efficiency, which proves that our crystal functions as a quantum storage device for polarization qubits. These results extend the storage capabilities of solid state quantum light matter interfaces to polarization encoding, which is widely used in quantum information science.


Experimental realization of light with time-separated correlations by rephasing amplified spontaneous emission.

Physical review letters 109 (2012) 093602-

PM Ledingham, WR Naylor, JJ Longdell

Amplified spontaneous emission is a common noise source in active optical systems, it is generally seen as being an incoherent process. Here we excite an ensemble of rare earth ion dopants in a solid with a π pulse, resulting in amplified spontaneous emission. The application of a second π pulse leads to a coherent echo of the amplified spontaneous emission that is correlated in both amplitude and phase. For small optical thicknesses, we see evidence that the amplified spontaneous emission and its echo are entangled.


Quantum storage of a photonic polarization qubit in a solid

Physical Review Letters 108 (2012)

M Gündoǧan, PM Ledingham, A Almasi, M Cristiani, H De Riedmatten

We report on the quantum storage and retrieval of photonic polarization quantum bits onto and out of a solid state storage device. The qubits are implemented with weak coherent states at the single photon level, and are stored for a predetermined time of 500 ns in a praseodymium doped crystal with a storage and retrieval efficiency of 10%, using the atomic frequency comb scheme. We characterize the storage by using quantum state tomography, and find that the average conditional fidelity of the retrieved qubits exceeds 95% for a mean photon number μ=0.4. This is significantly higher than a classical benchmark, taking into account the Poissonian statistics and finite memory efficiency, which proves that our crystal functions as a quantum storage device for polarization qubits. These results extend the storage capabilities of solid state quantum light matter interfaces to polarization encoding, which is widely used in quantum information science. © 2012 American Physical Society.


Compact Continuous-Variable Entanglement Distillation

PHYSICAL REVIEW LETTERS 108 (2012) ARTN 060502

A Datta, L Zhang, J Nunn, NK Langford, A Feito, MB Plenio, IA Walmsley


Controlled-NOT gate operating with single photons

APPLIED PHYSICS LETTERS 100 (2012) ARTN 211103

MA Pooley, DJP Ellis, RB Patel, AJ Bennett, KHA Chan, I Farrer, DA Ritchie, AJ Shields


Mapping coherence in measurement via full quantum tomography of a hybrid optical detector

Nature Photonics (2012)

L Zhang, HB Coldenstrodt-Ronge, A Datta, G Puentes, JS Lundeen, X-M Jin, BJ Smith, MB Plenio, IA Walmsley

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