A Noiseless Quantum Optical Memory at Room Temperature


PM Ledingham, KT Kaczmarek, B Brecht, A Feizpour, GS Thekkadath, SE Thomas, JHD Munns, DJ Saunders, J Nunn, IA Walmsley, IEEE

Quantum interference beyond the fringe.

Science (New York, N.Y.) 358 (2017) 1001-1002

I Walmsley

Temporal-mode selection with a Raman quantum memory

Optics InfoBase Conference Papers Part F66-FiO 2017 (2017)

JHD Munns, SE Thomas, KT Kaczmarek, PM Ledingham, DJ Saunders, J Nunn, B Brecht, IA Walmsley

© OSA 2017. Temporal modes (TMs) of pulsed single-photon states have been identified as appealing basis states for quantum information science. Recent work has seen progress towards TM-selective operations based on nonlinear optics. Here, we demonstrate for the first time a linear TM-selective device, namely a Raman quantum memory in warm atomic Caesium vapour. We achieve switching fidelities of 86.5% when operating the memory with ns-duration pulses. These results pave the way towards new quantum information applications, where TM-selection, TM-reshaping, and network synchronisation are achieved with one single device.

Resource-efficient fibre-integrated temporal multiplexing of heralded single photons

JOURNAL OF OPTICS 19 (2017) ARTN 125503

RA Hoggarth, RJA Francis-Jones, PJ Mosley

Fibre-integrated noise gating of high-purity heralded single photonsE

JOURNAL OF OPTICS 19 (2017) ARTN 104005

RJA Francis-Jones, PJ Mosley

Theory of noise suppression in Lambda-type quantum memories by means of a cavity

PHYSICAL REVIEW A 96 (2017) ARTN 012338

J Nunn, JHD Munns, S Thomas, KT Kaczmarek, C Qiu, A Feizpour, E Poem, B Brecht, DJ Saunders, PM Ledingham, DV Reddy, MG Raymer, IA Walmsley

A noiseless quantum optical memory at room temperature

Optics InfoBase Conference Papers Part F66-FiO 2017 (2017)

KT Kaczmarek, PM Ledingham, B Brecht, SE Thomas, GS Thekkadath, O Lazo-Arjona, JHD Munns, E Poem, A Feizpour, DJ Saunders, J Nunn, IA Walmsley

© OSA 2017. Quantum optical memories are devices that store quantum states of light, which can allow for the active synchronization of probabilistic events within large-scale quantum networks. Recent work on quantum memories have seen impressive quantum operation, albeit still suffering from noise on the output mode of the device. Here we demonstrate a noise-free quantum memory for light based on the off-resonant cascaded absorption of photons in a warm vapour of caesium atoms. The memory is characterized by measuring a noise floor of 8×10-6photons per pulse. We demonstrate genuine quantum operation by storing and recalling on-demand heralded single photons with a heralded second-order autocorrelation function of g(2)= 0:028±0:009.

Quantum Correlations between Single Telecom Photons and a Multimode On-Demand Solid-State Quantum Memory

PHYSICAL REVIEW X 7 (2017) ARTN 021028

A Seri, A Lenhard, D Rielander, M Gundogan, PM Ledingham, M Mazzera, H de Riedmatten

A noise-free quantum memory for broadband light at room temperature

Optics InfoBase Conference Papers Part F73-QIM 2017 (2017)

KT Kaczmarek, PM Ledingham, B Brecht, A Feizpour, GS Thekkadath, SE Thomas, JHD Munns, DJ Saunders, IA Walmsley, J Nunn

© OSA 2017. We have developed a novel protocol for broadband, noise-free light-matter interactions using off-resonant two-photon absorption. We have successfully stored and retrieved 1.5 GHz bandwidth heralded single photons in warm cesium vapour, measuring a g(2)h = 0:39±0:05.

Experimental demonstration of nonbilocal quantum correlations.

Science advances 3 (2017) e1602743-

DJ Saunders, DJ Saunders, AJ Bennet, C Branciard, GJ Pryde

Quantum mechanics admits correlations that cannot be explained by local realistic models. The most studied models are the standard local hidden variable models, which satisfy the well-known Bell inequalities. To date, most works have focused on bipartite entangled systems. We consider correlations between three parties connected via two independent entangled states. We investigate the new type of so-called "bilocal" models, which correspondingly involve two independent hidden variables. These models describe scenarios that naturally arise in quantum networks, where several independent entanglement sources are used. Using photonic qubits, we build such a linear three-node quantum network and demonstrate nonbilocal correlations by violating a Bell-like inequality tailored for bilocal models. Furthermore, we show that the demonstration of nonbilocality is more noise-tolerant than that of standard Bell nonlocality in our three-party quantum network.

QLad: A Noise-Free Quantum Memory for Broadband Light at Room Temperature


KT Kaczmarek, PM Ledingham, B Brecht, A Feizpour, GS Thekkadath, SE Thomas, JHD Munns, DJ Saunders, IA Walmsley, J Nunn, IEEE

High efficiency Raman memory by suppressing radiation trapping


SED Thomas, JHD Munns, KT Kaczmarek, C Qiu, B Brecht, A Feizpour, PM Ledingham, IA Walmsley, J Nunn, DJ Saunders

Chip-based array of near-identical, pure, heralded single-photon sources

OPTICA 4 (2017) 90-96

JB Spring, PL Mennea, BJ Metcalf, PC Humphreys, JC Gates, HL Rogers, C Soller, BJ Smith, WS Kolthammer, PGR Smith, IA Walmsley

Two-photon quantum walk in a multimode fiber.

Science Advances 2 (2016) e1501054-

H Defienne, M Barbieri, IA Walmsley, BJ Smith, S Gigan

Multiphoton propagation in connected structures-a quantum walk-offers the potential of simulating complex physical systems and provides a route to universal quantum computation. Increasing the complexity of quantum photonic networks where the walk occurs is essential for many applications. We implement a quantum walk of indistinguishable photon pairs in a multimode fiber supporting 380 modes. Using wavefront shaping, we control the propagation of the two-photon state through the fiber in which all modes are coupled. Excitation of arbitrary output modes of the system is realized by controlling classical and quantum interferences. This report demonstrates a highly multimode platform for multiphoton interference experiments and provides a powerful method to program a general high-dimensional multiport optical circuit. This work paves the way for the next generation of photonic devices for quantum simulation, computing, and communication.

Cavity-Enhanced Room-Temperature Broadband Raman Memory.

Physical review letters 116 (2016) 090501-

DJ Saunders, JHD Munns, TFM Champion, C Qiu, KT Kaczmarek, E Poem, PM Ledingham, IA Walmsley, J Nunn

Broadband quantum memories hold great promise as multiplexing elements in future photonic quantum information protocols. Alkali-vapor Raman memories combine high-bandwidth storage, on-demand readout, and operation at room temperature without collisional fluorescence noise. However, previous implementations have required large control pulse energies and have suffered from four-wave-mixing noise. Here, we present a Raman memory where the storage interaction is enhanced by a low-finesse birefringent cavity tuned into simultaneous resonance with the signal and control fields, dramatically reducing the energy required to drive the memory. By engineering antiresonance for the anti-Stokes field, we also suppress the four-wave-mixing noise and report the lowest unconditional noise floor yet achieved in a Raman-type warm vapor memory, (15±2)×10^{-3} photons per pulse, with a total efficiency of (9.5±0.5)%.

Nonclassicality Criteria in Multiport Interferometry.

Physical review letters 117 (2016) 213602-

L Rigovacca, C Di Franco, BJ Metcalf, IA Walmsley, MS Kim

Interference lies at the heart of the behavior of classical and quantum light. It is thus crucial to understand the boundaries between which interference patterns can be explained by a classical electromagnetic description of light and which, on the other hand, can only be understood with a proper quantum mechanical approach. While the case of two-mode interference has received a lot of attention, the multimode case has not yet been fully explored. Here we study a general scenario of intensity interferometry: we derive a bound on the average correlations between pairs of output intensities for the classical wavelike model of light, and we show how it can be violated in a quantum framework. As a consequence, this violation acts as a nonclassicality witness, able to detect the presence of sources with sub-Poissonian photon-number statistics. We also develop a criterion that can certify the impossibility of dividing a given interferometer into two independent subblocks.

Efficient and pure femtosecond-pulse-length source of polarization-entangled photons.

Optics express 24 (2016) 10869-10879

MM Weston, HM Chrzanowski, S Wollmann, A Boston, J Ho, LK Shalm, VB Verma, MS Allman, SW Nam, RB Patel, S Slussarenko, GJ Pryde

We present a source of polarization entangled photon pairs based on spontaneous parametric downconversion engineered for frequency uncorrelated telecom photon generation. Our source provides photon pairs that display, simultaneously, the key properties for high-performance quantum information and fundamental quantum science tasks. Specifically, the source provides for high heralding efficiency, high quantum state purity and high entangled state fidelity at the same time. Among different tests we apply to our source we observe almost perfect non-classical interference between photons from independent sources with a visibility of (100 ± 5)%.

Quantum Correlations from the Conditional Statistics of Incomplete Data.

Physical review letters 117 (2016) 083601-083601

J Sperling, TJ Bartley, G Donati, M Barbieri, X-M Jin, A Datta, W Vogel, IA Walmsley

We study, in theory and experiment, the quantum properties of correlated light fields measured with click-counting detectors providing incomplete information on the photon statistics. We establish a correlation parameter for the conditional statistics, and we derive the corresponding nonclassicality criteria for detecting conditional quantum correlations. Classical bounds for Pearson's correlation parameter are formulated that allow us, once they are violated, to determine nonclassical correlations via the joint statistics. On the one hand, we demonstrate nonclassical correlations in terms of the joint click statistics of light produced by a parametric down-conversion source. On the other hand, we verify quantum correlations of a heralded, split single-photon state via the conditional click statistics together with a generalization to higher-order moments. We discuss the performance of the presented nonclassicality criteria to successfully discern joint and conditional quantum correlations. Remarkably, our results are obtained without making any assumptions on the response function, quantum efficiency, and dark-count rate of photodetectors.

Enhanced delegated computing using coherence

PHYSICAL REVIEW A 93 (2016) ARTN 032339

S Barz, V Dunjko, F Schlederer, M Moore, E Kashefi, IA Walmsley

A Cavity-Enhanced Room-Temperature Broadband Raman Memory


PM Ledingham, JHD Munns, SE Thomas, TFM Champion, C Qiu, KT Kaczmarek, A Feizpour, E Poem, IA Walmsley, J Nunn, DJ Saunders, IEEE