Publications by Steven Kolthammer

High-birefringence direct UV-written waveguides for use as heralded single-photon sources at telecommunication wavelengths.

Optics express 26 (2018) 24678-24686

MT Posner, T Hiemstra, PL Mennea, RHS Bannerman, UB Hoff, A Eckstein, W Steven Kolthammer, IA Walmsley, DH Smith, JC Gates, PGR Smith

Direct UV-written waveguides are fabricated in silica-on-silicon with birefringence of (4.9 ± 0.2) × 10-4, much greater than previously reported in this platform. We show that these waveguides are suitable for the generation of heralded single photons at telecommunication wavelengths by spontaneous four-wave mixing. A pulsed pump field at 1060 nm generates pairs of photons in highly detuned, spectrally uncorrelated modes near 1550 nm and 800 nm. Waveguide-to-fiber coupling efficiencies of 78-91 % are achieved for all fields. Waveguide birefringence is controlled through dopant concentration of GeCl4 and BCl3 using the flame hydrolysis deposition process. The technology provides a route towards the scalability of silica-on-silicon integrated components for photonic quantum experiments.

Approximating vibronic spectroscopy with imperfect quantum optics


WR Clements, JJ Renema, A Eckstein, AA Valido, A Lita, T Gerrits, SW Nam, WS Kolthammer, J Huh, IA Walmsley

Efficient Classical Algorithm for Boson Sampling with Partially Distinguishable Photons.

Physical review letters 120 (2018) 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.

Optical nonclassicality test based on third-order intensity correlations

PHYSICAL REVIEW A 97 (2018) ARTN 033809

L Rigovacca, WS Kolthammer, C Di Franco, MS Kim

On-chip III-V monolithic integration of heralded single photon sources and beamsplitters


J Belhassen, F Baboux, Q Yao, M Amanti, I Favero, A Lemaitre, WS Kolthammer, IA Walmsley, S Ducci

Tensor network states in time-bin quantum optics

PHYSICAL REVIEW A 97 (2018) ARTN 062304

M Lubasch, AA Valido, JJ Renema, WS Kolthammer, D Jaksch, MS Kim, I Walmsley, R Garcia-Patron

Gaussian optical Ising machines

PHYSICAL REVIEW A 96 (2017) ARTN 043850

WR Clements, JJ Renema, YH Wen, HM Chrzanowski, WS Kolthammer, IA Walmsley

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

Distinguishability and Many-Particle Interference.

Physical review letters 118 (2017) 153603-

AJ Menssen, AE Jones, BJ Metcalf, MC Tichy, S Barz, WS Kolthammer, IA Walmsley

Quantum interference of two independent particles in pure quantum states is fully described by the particles' distinguishability: the closer the particles are to being identical, the higher the degree of quantum interference. When more than two particles are involved, the situation becomes more complex and interference capability extends beyond pairwise distinguishability, taking on a surprisingly rich character. Here, we study many-particle interference using three photons. We show that the distinguishability between pairs of photons is not sufficient to fully describe the photons' behavior in a scattering process, but that a collective phase, the triad phase, plays a role. We are able to explore the full parameter space of three-photon interference by generating heralded single photons and interfering them in a fiber tritter. Using multiple degrees of freedom-temporal delays and polarization-we isolate three-photon interference from two-photon interference. Our experiment disproves the view that pairwise two-photon distinguishability uniquely determines the degree of nonclassical many-particle interference.

Optimal design for universal multiport interferometers

OPTICA 3 (2016) 1460-1465

WR Clements, PC Humphreys, BJ Metcalf, WS Kolthammer, IA Walmsley

Quantum enhanced estimation of optical detector efficiencies

Quantum Measurements and Quantum Metrology Walter de Gruyter GmbH 3 (2016)

M Barbieri, A Datta, TJ Bartley, X-M Jin, WS Kolthammer, IA Walmsley

<jats:title>Abstract</jats:title><jats:p>Quantum mechanics establishes the ultimate limit to the scaling of the precision on any parameter, by identifying optimal probe states and measurements. While this paradigm is, at least in principle, adequate for the metrology of quantum channels involving the estimation of phase and loss parameters, we show that estimating the loss parameters associated with a quantum channel and a realistic quantum detector are fundamentally different. While Fock states are provably optimal for the former, we identify a crossover in the nature of the optimal probe state for estimating detector imperfections as a function of the loss parameter using Fisher information as a benchmark. We provide theoretical results for on-off and homodyne detectors, the most widely used detectors in quantum photonics technologies, when using Fock states and coherent states as probes.</jats:p>

Large scale quantum walks by means of optical fiber cavities

JOURNAL OF OPTICS 18 (2016) ARTN 094007

J Boutari, A Feizpour, S Barz, C Di Franco, MS Kim, WS Kolthammer, IA Walmsley

Large numbers of cold positronium atoms created in laser-selected Rydberg states using resonant charge exchange


R McConnell, G Gabrielse, WS Kolthammer, P Richerme, A Muellers, J Walz, D Grzonka, M Zielinski, D Fitzakerley, MC George, EA Hessels, CH Storry, M Weel, ATRAP Collaboration

Interfacing GHz-bandwidth heralded single photons with a warm vapour Raman memory


PS Michelberger, TFM Champion, MR Sprague, KT Kaczmarek, M Barbieri, XM Jin, DG England, WS Kolthammer, DJ Saunders, J Nunn, IA Walmsley

Tomography of photon-number resolving continuous-output detectors


PC Humphreys, BJ Metcalf, T Gerrits, T Hiemstra, AE Lita, J Nunn, SW Nam, A Datta, WS Kolthammer, IA Walmsley

Ultrahigh and persistent optical depths of cesium in Kagomé-type hollow-core photonic crystal fibers.

Optics letters 40 (2015) 5582-5585

KT Kaczmarek, DJ Saunders, MR Sprague, WS Kolthammer, A Feizpour, PM Ledingham, B Brecht, E Poem, IA Walmsley, J Nunn

Alkali-filled hollow-core fibers are a promising medium for investigating light-matter interactions, especially at the single-photon level, due to the tight confinement of light and high optical depths achievable by light-induced atomic desorption (LIAD). However, until now these large optical depths could only be generated for seconds, at most once per day, severely limiting the practicality of the technology. Here we report the generation of the highest observed transient (>10(5) for up to a minute) and highest observed persistent (>2000 for hours) optical depths of alkali vapors in a light-guiding geometry to date, using a cesium-filled Kagomé-type hollow-core photonic crystal fiber (HC-PCF). Our results pave the way to light-matter interaction experiments in confined geometries requiring long operation times and large atomic number densities, such as generation of single-photon-level nonlinearities and development of single photon quantum memories.

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

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

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.

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.