Publications


Enhancing multiphoton rates with quantum memories

Physical Review Letters 110 (2013)

J Nunn, NK Langford, WS Kolthammer, TFM Champion, MR Sprague, PS Michelberger, XM Jin, DG England, IA Walmsley

Single photons are a vital resource for optical quantum information processing. Efficient and deterministic single photon sources do not yet exist, however. To date, experimental demonstrations of quantum processing primitives have been implemented using nondeterministic sources combined with heralding and/or postselection. Unfortunately, even for eight photons, the data rates are already so low as to make most experiments impracticable. It is well known that quantum memories, capable of storing photons until they are needed, are a potential solution to this "scaling catastrophe." Here, we analyze in detail the benefits of quantum memories for producing multiphoton states, showing how the production rates can be enhanced by many orders of magnitude. We identify the quantity ηB as the most important figure of merit in this connection, where η and B are the efficiency and time-bandwidth product of the memories, respectively. © 2013 American Physical Society.


Sequential path entanglement for quantum metrology

Scientific Reports 3 (2013)

XM Jin, CZ Peng, Y Deng, M Barbieri, J Nunn, IA Walmsley

Path entanglement is a key resource for quantum metrology. Using path-entangled states, the standard quantum limit can be beaten, and the Heisenberg limit can be achieved. However, the preparation and detection of such states scales unfavourably with the number of photons. Here we introduce sequential path entanglement, in which photons are distributed across distinct time bins with arbitrary separation, as a resource for quantum metrology. We demonstrate a scheme for converting polarization Greenberger-Horne-Zeilinger entanglement into sequential path entanglement. We observe the same enhanced phase resolution expected for conventional path entanglement, independent of the delay between consecutive photons. Sequential path entanglement can be prepared comparably easily from polarization entanglement, can be detected without using photon-number-resolving detectors, and enables novel applications.


Hybrid optical and electronic laser locking using slow light due to spectral holes

PHYSICAL REVIEW A 87 (2013) ARTN 063824

JW Tay, WG Farr, PM Ledingham, D Korystov, JJ Longdell


Coherent storage of temporally multimode light using a spin-wave atomic frequency comb memory

NEW JOURNAL OF PHYSICS 15 (2013) ARTN 045012

M Guendogan, M Mazzera, PM Ledingham, M Cristiani, H de Riedmatten


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


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


Recursive quantum detector tomography

NEW JOURNAL OF PHYSICS 14 (2012) ARTN 115005

L Zhang, A Datta, HB Coldenstrodt-Ronge, X-M Jin, J Eisert, MB Plenio, IA Walmsley


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.


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


Multiphoton state engineering by heralded interference between single photons and coherent states

Phys. Rev. A American Physical Society 86 (2012) 043820-043820

TJ Bartley, G Donati, JB Spring, X-M Jin, M Barbieri, A Datta, BJ Smith, IA Walmsley


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

Phys. Rev. Lett. American Physical Society 108 (2012) 263602-263602

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

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