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.

A solid state spin-wave quantum memory for photonic time-Bin qubits

Optics InfoBase Conference Papers (2014)

M Gündogan, K Kutluer, PM Ledingham, M Mazzera, H de Riedmatten

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.

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

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


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


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


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


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

Quantum storage of heralded single photons in a praseodymium-doped crystal.

Physical review letters 112 (2014) 040504-

D Rieländer, K Kutluer, PM Ledingham, M Gündoğan, J Fekete, M Mazzera, H de Riedmatten

We report on experiments demonstrating the reversible mapping of heralded single photons to long-lived collective optical atomic excitations stored in a Pr3+:Y2SiO5 crystal. A cavity-enhanced spontaneous down-conversion source is employed to produce widely nondegenerate narrow-band (≈2  MHz) photon pairs. The idler photons, whose frequency is compatible with telecommunication optical fibers, are used to herald the creation of the signal photons, compatible with the Pr3+ transition. The signal photons are stored and retrieved using the atomic frequency comb protocol. We demonstrate storage times up to 4.5  μs while preserving nonclassical correlations between the heralding and the retrieved photon. This is more than 20 times longer than in previous realizations in solid state devices, and implemented in a system ideally suited for the extension to spin-wave storage.

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

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.

A solid state spin-wave quantum memory for photonic time-Bin qubits

Optics InfoBase Conference Papers Part F3-EQEC 2015 (2014)

M Gündogan, K Kutluer, PM Ledingham, M Mazzera, H de Riedmatten

Ultrasonically assisted deposition of colloidal crystals


S Wollmann, RB Patel, A Wixforth, HJ Krenner

Strain-optic active control for quantum integrated photonics.

Optics express 22 (2014) 21719-21726

PC Humphreys, BJ Metcalf, JB Spring, M Moore, PS Salter, MJ Booth, W Steven Kolthammer, IA Walmsley

We present a practical method for active phase control on a photonic chip that has immediate applications in quantum photonics. Our approach uses strain-optic modification of the refractive index of individual waveguides, effected by a millimeter-scale mechanical actuator. The resulting phase change of propagating optical fields is rapid and polarization-dependent, enabling quantum applications that require active control and polarization encoding. We demonstrate strain-optic control of non-classical states of light in silica, showing the generation of 2-photon polarisation N00N states by manipulating Hong-Ou-Mandel interference. We also demonstrate switching times of a few microseconds, which are sufficient for silica-based feed-forward control of photonic quantum states.

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.

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

Mutual interferometric characterization of a pair of independent electric fields.

Opt Lett 38 (2013) 5299-5302

C Bourassin-Bouchet, MM Mang, I Gianani, IA Walmsley

We demonstrate a novel interferometric characterization scheme that allows the complete reconstruction of two interfering electric fields. The phase profiles of both beams, and their relative phase, can be retrieved simultaneously as a function of any degree of freedom in which it is possible to shear one of the beams. The method has applications in wavefront sensing or ultrashort-pulse measurement, especially also in the domain of extreme light sources where it is difficult to generate a reference field or to replicate the beam in order to perform a self-referencing measurement. We demonstrate the technique experimentally by measuring simultaneously two ultrashort pulses in a single laser shot.