Publications


Quantum-enhanced stimulated emission detection for label-free microscopy

APPLIED PHYSICS LETTERS 117 (2020) ARTN 024002

GT Garces, HM Chrzanowski, S Daryanoosh, V Thiel, AL Marchant, RB Patel, PC Humphreys, A Datta, IA Walmsley


Detector-agnostic phase-space distributions

Physical Review Letters American Physical Society 124 (2020) 013605

J Sperling, D Phillips, JFF Bulmer, GS Thekkadath, A Eckstein, TAW Wolterink, J Lugani, SW Nam, A Lita, T Gerrits, W Vogel, GS Agarwal, C Silberhorn, IA Walmsley

The representation of quantum states via phase-space functions constitutes an intuitive technique to characterize light. However, the reconstruction of such distributions is challenging as it demands specific types of detectors and detailed models thereof to account for their particular properties and imperfections. To overcome these obstacles, we derive and implement a measurement scheme that enables a reconstruction of phase-space distributions for arbitrary states whose functionality does not depend on the knowledge of the detectors, thus defining the notion of detector-agnostic phase-space distributions. Our theory presents a generalization of well-known phase-space quasiprobability distributions, such as the Wigner function. We implement our measurement protocol, using state-of-the-art transition-edge sensors without performing a detector characterization. Based on our approach, we reveal the characteristic features of heralded single- and two-photon states in phase space and certify their nonclassicality with high statistical significance.


Experimental Observation of Coherent-Information Superadditivity in a Dephrasure Channel.

Physical review letters 125 (2020) 060502-

S Yu, Y Meng, RB Patel, Y-T Wang, Z-J Ke, W Liu, Z-P Li, Y-Z Yang, W-H Zhang, J-S Tang, C-F Li, G-C Guo

We present an experimental approach to construct a dephrasure channel that contains both dephasing and erasure noises and can be used as an efficient tool to study the superadditivity of coherent information. Using a three-fold dephrasure channel, the superadditivity of coherent information is observed, and a substantial gap is found between the zero single-letter coherent information and zero quantum capacity. Particularly, we find that, when the coherent information of n channel uses is zero, with a larger number of channel uses the quantum capacity becomes positive. These phenomena exhibit a more obvious superadditivity of coherent information than previous works and demonstrate a higher threshold for nonzero quantum capacity. Such novel channels built in our experiment also can provide a useful platform to study the nonadditive properties of coherent information and quantum channel capacity.


Dimensional Quantum Memory Advantage in the Simulation of Stochastic Processes

Physical Review Letters American Physical Society (2019)

F Ghafari, N Tischler, J Thompson, M Gu, LK Shalm, VB Verma, SW Nam, RAJ Patel, HM Wiseman, GJ Pryde

Stochastic processes underlie a vast range of natural and social phenomena. Some processes such as atomic decay feature intrinsic randomness, whereas other complex processes, e.g. traffic congestion, are effectively probabilistic because we cannot track all relevant variables. To simulate a stochastic system's future behaviour, information about its past must be stored and thus memory is a key resource. Quantum information processing promises a memory advantage for stochastic simulation that has been validated in recent proof-of-concept experiments. Yet, in all past works, the memory saving would only become accessible in the limit of a large number of parallel simulations, because the memory registers of individual quantum simulators had the same dimensionality as their classical counterparts. Here, we report the first experimental demonstration that a quantum stochastic simulator can encode the relevant information in fewer dimensions than any classical simulator, thereby achieving a quantum memory advantage even for an individual simulator. Our photonic experiment thus establishes the potential of a new, practical resource saving in the simulation of complex systems.


Raman quantum memory with built-in suppression of four-wave-mixing noise

Physical Review A American Physical Society 100 (2019) 033801

Thomas, T Hird, J Munns, B Brecht, D Saunders, J Nunn, IA Walmsley, PM Ledingham

Quantum memories are essential for large-scale quantum information networks. Along with high efficiency, storage lifetime, and optical bandwidth, it is critical that the memory adds negligible noise to the recalled signal. A common source of noise in optical quantum memories is spontaneous four-wave mixing. We develop and implement a technically simple scheme to suppress this noise mechanism by means of quantum interference. Using this scheme with a Raman memory in warm atomic vapor, we demonstrate over an order of magnitude improvement in noise performance. Furthermore we demonstrate a method to quantify the remaining noise contributions and present a route to enable further noise suppression. Our scheme opens the way to quantum demonstrations using a broadband memory, significantly advancing the search for scalable quantum photonic networks.


Benchmarking of Gaussian boson sampling using two-point correlators

Physical Review A American Physical Society (APS) 99 (2019) 023836

DS Phillips, M Walschaers, JJ Renema, IA Walmsley, N Treps, J Sperling


An experimental quantum Bernoulli factory

Science Advances American Association for the Advancement of Science (AAAS) 5 (2019) eaau6668-eaau6668

RB Patel, T Rudolph, GJ Pryde

<jats:p>There has been a concerted effort to identify problems computable with quantum technology, which are intractable with classical technology or require far fewer resources to compute. Recently, randomness processing in a Bernoulli factory has been identified as one such task. Here, we report two quantum photonic implementations of a Bernoulli factory, one using quantum coherence and single-qubit measurements and the other one using quantum coherence and entangling measurements of two qubits. We show that the former consumes three orders of magnitude fewer resources than the best-known classical method, while entanglement offers a further fivefold reduction. These concepts may provide a means for quantum-enhanced performance in the simulation of stochastic processes and sampling tasks.</jats:p>


Efficient Classical Algorithm for Boson Sampling with Partially Distinguishable Photons.

Phys Rev Lett 120 (2018) 220502-220502

JJ Renema, A Menssen, WR Clements, G Triginer, WS Kolthammer, IA Walmsley

We demonstrate how boson sampling with photons of partial distinguishability can be expressed in terms of interference of fewer photons. We use this observation to propose a classical algorithm to simulate the output of a boson sampler fed with photons of partial distinguishability. We find conditions for which this algorithm is efficient, which gives a lower limit on the required indistinguishability to demonstrate a quantum advantage. Under these conditions, adding more photons only polynomially increases the computational cost to simulate a boson sampling experiment.


Engineering a noiseless and broadband Raman quantum memory for temporal mode manipulation

Frontiers in Optics / Laser Science Part F114-FIO 2018 (2018)

TM Hird, S THOMAS, J MUNNS, J Nunn, O Arjona, S Gao, B Brecht, PM Ledingham, IAN WALMSLEY

© 2018 The Author(s). The Raman quantum memory can manipulate temporal modes of light - a promising high-dimensional basis for quantum information processing. We demonstrate both temporal mode manipulation and a novel suppression scheme for four-wave mixing noise.


Reference-frame-independent Einstein-Podolsky-Rosen steering

PHYSICAL REVIEW A 98 (2018) ARTN 022333

S Wollmann, MJW Hall, RB Patel, HM Wiseman, GJ Pryde


Conclusive experimental demonstration of one-way Einstein-Podolsky-Rosen steering

Phys. Rev. Lett. 121 (2018) 100401-100401

N Tischler, F Ghafari, TJ Baker, S Slussarenko, RB Patel, MM Weston, S Wollmann, LK Shalm, VB Verma, SW Nam, HC Nguyen, HM Wiseman, GJ Pryde

Einstein-Podolsky-Rosen steering is a quantum phenomenon wherein one party influences, or steers, the state of a distant party's particle beyond what could be achieved with a separable state, by making measurements on one half of an entangled state. This type of quantum nonlocality stands out through its asymmetric setting, and even allows for cases where one party can steer the other, but where the reverse is not true. A series of experiments have demonstrated one-way steering in the past, but all were based on significant limiting assumptions. These consisted either of restrictions on the type of allowed measurements, or of assumptions about the quantum state at hand, by mapping to a specific family of states and analysing the ideal target state rather than the real experimental state. Here, we present the first experimental demonstration of one-way steering free of such assumptions. We achieve this using a new sufficient condition for non-steerability, and, although not required by our analysis, using a novel source of extremely high-quality photonic Werner states.


Challenging local realism with human choices

NATURE 557 (2018) 212-+

C Abellan, A Acin, A Alarcon, O Alibart, CK Andersen, F Andreoli, A Beckert, FA Beduini, A Bendersky, M Bentivegna, P Bierhorst, D Burchardt, A Cabello, J Carine, S Carrasco, G Carvacho, D Cavalcanti, R Chaves, J Cortes-Vega, A Cuevas, A Delgado, H de Riedmatten, C Eichler, P Farrera, J Fuenzalida, M Garcia-Matos, R Garthoff, S Gasparinetti, T Gerrits, FG Jouneghani, S Glancy, ES Gomez, P Gonzalez, J-Y Guan, J Handsteiner, J Heinsoo, G Heinze, A Hirschmann, O Jimenez, F Kaiser, E Knill, LT Knoll, S Krinner, P Kurpiers, MA Larotonda, J-A Larsson, A Lenhard, H Li, M-H Li, G Lima, B Liu, Y Liu, IH Lopez Grande, T Lunghi, X Ma, OS Magana-Loaiza, P Magnard, A Magnoni, M Marti-Prieto, D Martinez, P Mataloni, A Mattar, M Mazzera, RP Mirin, MW Mitchell, S Nam, M Oppliger, J-W Pan, RB Patel, GJ Pryde, D Rauch, K Redeker, D Rielander, M Ringbauer, T Roberson, W Rosenfeld, Y Salathe, L Santodonato, G Sauder, T Scheidl, CT Schmiegelow, F Sciarrino, A Seri, LK Shalm, S-C Shi, S Slussarenko, MJ Stevens, S Tanzilli, F Toledo, J Tura, R Ursin, P Vergyris, VB Verma, T Walter, A Wallraff, Z Wang, H Weinfurter, MM Weston, AG White, C Wu, GB Xavier, L You, X Yuan, A Zeilinger, Q Zhang, W Zhang, J Zhong, BIGBT Collaboration


Strong Unitary and Overlap Uncertainty Relations: Theory and Experiment

PHYSICAL REVIEW LETTERS 120 (2018) ARTN 230402

K-W Bong, N Tischler, RB Patel, S Wollmann, GJ Pryde, MJW Hall


Quantum interference beyond the fringe.

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

I Walmsley


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

Optica Optical Society of America 4 (2017) 90-96

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

Interference between independent single photons is perhaps the most fundamental interaction in quantum optics. It has become increasingly important as a tool for optical quantum information science, as one of the rudimentary quantum operations, together with photon detection, for generating entanglement between non-interacting particles. Despite this, demonstrations of large-scale photonic networks involving more than two independent sources of quantum light have been limited due to the difficulty in constructing large arrays of high-quality, single-photon sources. Here, we solve the key challenge, reporting on a novel array of five near-identical, low-loss, high-purity, heralded single-photon sources using spontaneous four-wave mixing on a silica chip. We verify source quality through a series of heralded Hong–Ou–Mandel (HOM) experiments, and further report the experimental three-photon extension of the HOM interference effect, which maps out for the first time, to our knowledge, the interference landscape between three independent single-photon sources.


Editorial: Building Quantum Networks

PHYSICAL REVIEW APPLIED 6 (2016) ARTN 040001

IA Walmsley, J Nunn


Nonclassicality Criteria in Multiport Interferometry

Physical Review Letters American Physical Society 117 (2016)

L Rigovacca, C Di Franco, BJ Metcalf, I 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.


A quantum Fredkin gate (Conference Presentation)

Quantum Information Science and Technology II SPIE (2016)

RB Patel, J Ho, F Ferreyrol, TC Ralph, GJ Pryde

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