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Atomic and Laser Physics
Credit: Jack Hobhouse

Ian Walmsley

Visiting Professor Division

Sub department

  • Atomic and Laser Physics
Ian.Walmsley@physics.ox.ac.uk
  • About
  • Publications

Efficient Classical Algorithm for Boson Sampling with Partially Distinguishable Photons.

Phys Rev Lett 120:22 (2018) 220502-220502

Authors:

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

Abstract:

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.
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Quantum interference beyond the fringe.

Science (New York, N.Y.) 358:6366 (2017) 1001-1002
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Chip-based array of near-identical, pure, heralded single-photon sources

Optica Optical Society of America 4:1 (2017) 90-96

Authors:

Justin B Spring, PL Mennea, Benjamin J Metcalf, Peter C Humphreys, JC Gates, HL Rogers, Christoph Söller, Brian J Smith, W Steven Kolthammer, Peter GR Smith, Ian A Walmsley

Abstract:

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.
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Nonclassicality Criteria in Multiport Interferometry

Physical Review Letters American Physical Society 117:21 (2016)

Authors:

L Rigovacca, C Di Franco, Benjamin J Metcalf, Ian Walmsley, MS Kim

Abstract:

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.
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Editorial: Building Quantum Networks

PHYSICAL REVIEW APPLIED 6:4 (2016) ARTN 040001

Authors:

IA Walmsley, J Nunn
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