Publications


Observing optical coherence across Fock layers with weak-field homodyne detectors.

Nature communications 5 (2014) 5584-

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

Quantum properties of optical modes are typically assessed by observing their photon statistics or the distribution of their quadratures. Both particle- and wave-like behaviours deliver important information and each may be used as a resource in quantum-enhanced technologies. Weak-field homodyne (WFH) detection provides a scheme that combines the wave- and particle-like descriptions. Here we show that it is possible to observe a wave-like property such as the optical coherence across Fock basis states in the detection statistics derived from discrete photon counting. We experimentally demonstrate these correlations using two WHF detectors on each mode of two classes of two-mode entangled states. Furthermore, we theoretically describe the response of WHF detection on a two-mode squeezed state in the context of generalized Bell inequalities. Our work demonstrates the potential of this technique as a tool for hybrid continuous/discrete-variable protocols on a phenomenon that explicitly combines both approaches.


Simultaneous spatial characterization of two independent sources of high harmonic radiation.

Optics letters 39 (2014) 6142-6145

MM Mang, C Bourassin-Bouchet, IA Walmsley

We present the simultaneous spatial characterization of two independent sources of high harmonic radiation from a series of interferograms. Our technique transfers the necessity of replicating and shearing the test beam to a second, independent beam that may be easier to manipulate, and thus opens the possibility to characterize complex light sources. We demonstrate our technique by reconstructing the wavefronts of two high harmonic beams and use this information to study the spatial properties of different quantum paths.


Nonclassical light manipulation in a multiple-scattering medium.

Optics letters 39 (2014) 6090-6093

H Defienne, M Barbieri, B Chalopin, B Chatel, IA Walmsley, BJ Smith, S Gigan

We investigate the possibility of using a scattering medium as a highly multimode platform for implementing quantum walks. We demonstrate the manipulation of a single photon propagating through a strongly scattering medium using wavefront-shaping technique. Measurement of the scattering matrix allows the wavefront of the photon to be shaped to compensate the distortions induced by multiple scattering events. The photon can thus be directed coherently to a specific output mode. Using this approach, we show how entanglement of a single photon across different modes can be manipulated despite the enormous wavefront disturbance caused by the scattering medium.


Phase transitions in the brominated ferroelectric tris-sarcosine calcium chloride.

Advanced materials (Deerfield Beach, Fla.) 26 (2014) 3860-3866

JC Lashley, JHD Munns, M Echizen, MN Ali, SE Rowley, JF Scott


Broadband single-photon-level memory in a hollow-core photonic crystal fibre

NATURE PHOTONICS 8 (2014) 287-291

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


Broadband single-photon-level memory in a hollow-core photonic crystal fibre

Nature Photonics 8 (2014) 287-291

MR Sprague, PS Michelberger, TFM Champion, DG England, J Nunn, XM Jin, WS Kolthammer, A Abdolvand, PSJ Russell, IA Walmsley

Storing information encoded in light is critical for realizing optical buffers for all-optical signal processing and quantum memories for quantum information processing. These proposals require efficient interaction between atoms and a well-defined optical mode. Photonic crystal fibres can enhance light-matter interactions and have engendered a broad range of nonlinear effects; however, the storage of light has proven elusive. Here, we report the first demonstration of an optical memory in a hollow-core photonic crystal fibre. We store gigahertz-bandwidth light in the hyperfine coherence of caesium atoms at room temperature using a far-detuned Raman interaction. We demonstrate a signal-to-noise ratio of 2.6:1 at the single-photon level and a memory efficiency of 27 ± 1%. Our results demonstrate the potential of a room-temperature fibre-integrated optical memory for implementing local nodes of quantum information networks. © 2014 Macmillan Publishers Limited. All rights reserved.


Quantum estimation of the Schwarzschild spacetime parameters of the Earth

PHYSICAL REVIEW D 90 (2014) ARTN 124001

DE Bruschi, A Datta, R Ursin, TC Ralph, I Fuentes


Quantum discord in quantum information theory - From strong subadditivity to the mother protocol

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 6745 LNCS (2014) 188-197

V Madhok, A Datta

Positivity of quantum discord is shown to be equivalent to the strong sub additivity of the von Neumann entropy. This leads to a connection between the mother protocol of quantum information theory [17] and quantum discord. We exploit this to show that discord is a measure coherence in the performance of the mother protocol. Since the mother protocol is a unification of an important class of problems (those that are bipartite, unidirectional and memoryless), we show discord to be a measure of coherence in these protocols. Our work generalizes an earlier operational interpretation of discord provided in terms of quantum state merging [10]. © 2014 Springer-Verlag Berlin Heidelberg.


Heralded single photon storage in a room-temperature, broadband quantum memory

2014 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) (2014)

PS Michelberger, J Nunn, TFM Champion, MR Sprague, K Kacmarek, D Saunders, WS Kolthammer, X-M Jin, DG England, IA Walmsley, IEEE


Manipulating a non-classical state of light propagating through a multiply scattering medium

2014 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) (2014)

H Defienne, M Barbieri, B Chalopin, B Chatel, I Walmsley, B Smith, S Gigan, IEEE


Characterizing the variation of propagation constants in multicore fiber.

Optics express 22 (2014) 25689-25699

PJ Mosley, I Gris-Sánchez, JM Stone, RJA Francis-Jones, DJ Ashton, TA Birks

We demonstrate a numerical technique that can evaluate the core-to-core variations in propagation constant in multicore fiber. Using a Markov Chain Monte Carlo process, we replicate the interference patterns of light that has coupled between the cores during propagation. We describe the algorithm and verify its operation by successfully reconstructing target propagation constants in a fictional fiber. Then we carry out a reconstruction of the propagation constants in a real fiber containing 37 single-mode cores. We find that the range of fractional propagation constant variation across the cores is approximately ± 2 × 10(-5).


Photon-pair generation in photonic crystal fibre with a 1.5 GHz modelocked VECSEL

OPTICS COMMUNICATIONS 327 (2014) 39-44

OJ Morris, RJA Francis-Jones, KG Wilcox, AC Tropper, PJ Mosley


Joint estimation of phase and phase diffusion for quantum metrology.

Nature communications 5 (2014) 3532-

MD Vidrighin, G Donati, MG Genoni, X-M Jin, WS Kolthammer, MS Kim, A Datta, M Barbieri, IA Walmsley

Phase estimation, at the heart of many quantum metrology and communication schemes, can be strongly affected by noise, whose amplitude may not be known, or might be subject to drift. Here we investigate the joint estimation of a phase shift and the amplitude of phase diffusion at the quantum limit. For several relevant instances, this multiparameter estimation problem can be effectively reshaped as a two-dimensional Hilbert space model, encompassing the description of an interferometer phase probed with relevant quantum states--split single-photons, coherent states or N00N states. For these cases, we obtain a trade-off bound on the statistical variances for the joint estimation of phase and phase diffusion, as well as optimum measurement schemes. We use this bound to quantify the effectiveness of an actual experimental set-up for joint parameter estimation for polarimetry. We conclude by discussing the form of the trade-off relations for more general states and measurements.


Storage of up-converted telecom photons in a doped crystal

NEW JOURNAL OF PHYSICS 16 (2014) ARTN 113021

N Maring, K Kutluer, J Cohen, M Cristiani, M Mazzera, PM Ledingham, H de Riedmatten


Quantum teleportation on a photonic chip

NATURE PHOTONICS 8 (2014) 770-774

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


Identifying nonclassicality of multiphoton and multimode quantum states directly from experimental detector outcomes

Frontiers in Optics, FiO 2014 (2014)

TJ Bartley, G Donati, XM Jin, A Datta, M Barbieri, IA Walmsley

We show experimentally how nonclassical statistics arise directly from the joint outcomes of multiplexed on-off detectors on two-mode, multiphoton optical states. This identifies a possible route to an entanglement witness using this scheme.


Tradeoff in simultaneous quantum-limited phase and loss estimation in interferometry

PHYSICAL REVIEW A 89 (2014) ARTN 023845

PJD Crowley, A Datta, M Barbieri, IA Walmsley


Storing GHz bandwidth heralded single photons in a room-temperature raman memory: Efficiency and noise

Optics InfoBase Conference Papers (2014)

J Nunn, PS Michelberger, TFM Champion, MR Sprague, K Kacmarek, D Saunders, WS Kolthammer, XM Jin, DG England, IA Walmsley

We store GHz-bandwidth heralded single photons in a room-temperature Raman memory, which is a crucial primitive for scalable quantum photonics. We discuss methods to suppress four-wave mixing noise, which accompanies the retrieved photons. © 2014 Optical Society of America.


Continuous-variable quantum computing in optical time-frequency modes using quantum memories.

Physical review letters 113 (2014) 130502-

PC Humphreys, WS Kolthammer, J Nunn, M Barbieri, A Datta, IA Walmsley

We develop a scheme for time-frequency encoded continuous-variable cluster-state quantum computing using quantum memories. In particular, we propose a method to produce, manipulate, and measure two-dimensional cluster states in a single spatial mode by exploiting the intrinsic time-frequency selectivity of Raman quantum memories. Time-frequency encoding enables the scheme to be extremely compact, requiring a number of memories that are a linear function of only the number of different frequencies in which the computational state is encoded, independent of its temporal duration. We therefore show that quantum memories can be a powerful component for scalable photonic quantum information processing architectures.


Continuous-variable quantum computing in optical time-frequency modes using quantum memories

Physical Review Letters 113 (2014)

PC Humphreys, WS Kolthammer, J Nunn, M Barbieri, A Datta, IA Walmsley

© 2014 American Physical Society. We develop a scheme for time-frequency encoded continuous-variable cluster-state quantum computing using quantum memories. In particular, we propose a method to produce, manipulate, and measure two-dimensional cluster states in a single spatial mode by exploiting the intrinsic time-frequency selectivity of Raman quantum memories. Time-frequency encoding enables the scheme to be extremely compact, requiring a number of memories that are a linear function of only the number of different frequencies in which the computational state is encoded, independent of its temporal duration. We therefore show that quantum memories can be a powerful component for scalable photonic quantum information processing architectures.

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