Publications


Non-Classical States Of Light: Toward Scalable Photonic Quantum Networks

2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) (2013)

IA Walmsley, IEEE


Surpassing the conventional Heisenberg limit using classical resources

2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) (2013)

X-M Jin, M Lebrat, L Zhang, K Lee, T Bartley, M Barbieri, J Nunn, A Datta, IA Walmsley, IEEE


Quantum memories and large-scale quantum coherence based on Raman interactions

2013 IEEE PHOTONICS SOCIETY SUMMER TOPICAL MEETING SERIES (2013) 173-+

J Nunn, MR Sprague, PS Michelberger, TFM Champion, X-M Jin, NK Langford, BJ Sussman, DG England, M Barbieri, WS Kolthammer, IA Walmsley, IEEE


Boson sampling on a photonic chip.

Science 339 (2013) 798-801

JB Spring, BJ Metcalf, PC Humphreys, WS Kolthammer, X-M Jin, M Barbieri, A Datta, N Thomas-Peter, NK Langford, D Kundys, JC Gates, BJ Smith, PGR Smith, IA Walmsley

Although universal quantum computers ideally solve problems such as factoring integers exponentially more efficiently than classical machines, the formidable challenges in building such devices motivate the demonstration of simpler, problem-specific algorithms that still promise a quantum speedup. We constructed a quantum boson-sampling machine (QBSM) to sample the output distribution resulting from the nonclassical interference of photons in an integrated photonic circuit, a problem thought to be exponentially hard to solve classically. Unlike universal quantum computation, boson sampling merely requires indistinguishable photons, linear state evolution, and detectors. We benchmarked our QBSM with three and four photons and analyzed sources of sampling inaccuracy. Scaling up to larger devices could offer the first definitive quantum-enhanced computation.


High-efficiency Bragg Grating Enhanced On-chip Photon-number-resolving Detectors

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

PL Mennea, B Calkins, BJ Metcalf, T Gerrits, AE Lita, JC Gates, WS Kolthammer, JB Spring, PC Humphries, NA Tomlin, AE Fox, AL Linares, RP Mirin, SW Nam, IA Walmsley, PGR Smith, IEEE


Direct observation of sub-binomial light

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


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


Spin-wave storage of single photon level light fields in a doped solid

Optics InfoBase Conference Papers (2013)

M Gündoǧan, D Rieländer, K Kutluer, J Fekete, PM Ledingham, M Mazzera, M Cristiani, H De Riedmatten

We present optical storage experiments with weak coherent states and heralded single photons by using the atomic frequency comb technique in the long-lived hyperfine levels in an ensemble of Pr3+ ions doped into a solid. © OSA 2013.


Storage of Light in a Hollow-Core Photonic-Crystal Fibre

2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) (2013)

MR Sprague, P Michelberger, TFM Champion, DG England, J Nunn, WS Kolthammer, X-M Jin, A Abdolvand, PSJ Russell, 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


Quantum detector tomography of a time-multiplexed superconducting nanowire single-photon detector at telecom wavelengths

Optics Express 21 (2013) 893-902

CM Natarajan, L Zhang, H Coldenstrodt-Ronge, G Donati, SN Dorenbos, V Zwiller, IA Walmsley, RH Hadfield

Superconducting nanowire single-photon detectors (SNSPDs) are widely used in telecom wavelength optical quantum information science applications. Quantum detector tomography allows the positive-operator-valued measure (POVM) of a single-photon detector to be determined. We use an all-fiber telecom wavelength detector tomography test bed to measure detector characteristics with respect to photon flux and polarization, and hence determine the POVM. We study the SNSPD both as a binary detector and in an 8-bin, fiber based, Time-Multiplexed (TM) configuration at repetition rates up to 4 MHz. The corresponding POVMs provide an accurate picture of the photon number resolving capability of the TM-SNSPD. © 2013 Optical Society of America.


Strategies for enhancing quantum entanglement by local photon subtraction

Physical Review A - Atomic, Molecular, and Optical Physics 87 (2013)

TJ Bartley, PJD Crowley, A Datta, J Nunn, L Zhang, I Walmsley

Subtracting photons from a two-mode squeezed state is a well-known method to increase entanglement. We analyze different strategies of local photon subtraction from a two-mode squeezed state in terms of entanglement gain and success probability. We develop a general framework that incorporates imperfections and losses in all stages of the process: before, during, and after subtraction. By combining all three effects into a single efficiency parameter, we provide analytical and numerical results for subtraction strategies using photon-number-resolving and threshold detectors. We compare the entanglement gain afforded by symmetric and asymmetric subtraction scenarios across the two modes. For a given amount of loss, we identify an optimized set of parameters, such as initial squeezing and subtraction beam splitter transmissivity, that maximize the entanglement gain rate. We identify regimes for which asymmetric subtraction of different Fock states on the two modes outperforms symmetric strategies. In the lossless limit, subtracting a single photon from one mode always produces the highest entanglement gain rate. In the lossy case, the optimal strategy depends strongly on the losses on each mode individually, such that there is no general optimal strategy. Rather, taking losses on each mode as the only input parameters, we can identify the optimal subtraction strategy and required beam splitter transmissivities and initial squeezing parameter. Finally, we discuss the implications of our results for the distillation of continuous-variable quantum entanglement. © 2013 American Physical Society.


High quantum efficiency photon-number-resolving detector for photonic on-chip information processing

2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) (2013)

B Calkins, PL Mennea, AE Lita, BJ Metcalf, WS Kolthammer, AL Linares, JB Spring, PC Humphreys, RP Mirin, JC Gates, PGR Smith, IA Walmsley, T Gerrits, SW Nam, 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.


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


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.


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.


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

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