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Adaptive Optical Phase Estimation Using Time-Symmetric Quantum Smoothing

T. A. Wheatley, D. W. Berry, H. Yonezawa, D. Nakane, H. Arao, D. T. Pope, T. C. Ralph, H. M. Wiseman, A. Furusawa, and E. H. Huntington
Phys. Rev. Lett. 104, 093601 – Published 3 March 2010
Physics logo See Synopsis: A smoother quantum measurement

Abstract

Quantum parameter estimation has many applications, from gravitational wave detection to quantum key distribution. The most commonly used technique for this type of estimation is quantum filtering, using only past observations. We present the first experimental demonstration of quantum smoothing, a time-symmetric technique that uses past and future observations, for quantum parameter estimation. We consider both adaptive and nonadaptive quantum smoothing, and show that both are better than their filtered counterparts. For the problem of estimating a stochastically varying phase shift on a coherent beam, our theory predicts that adaptive quantum smoothing (the best scheme) gives an estimate with a mean-square error up to 22 times smaller than nonadaptive filtering (the standard quantum limit). The experimentally measured improvement is 2.24±0.14.

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  • Received 6 December 2009

DOI:https://doi.org/10.1103/PhysRevLett.104.093601

©2010 American Physical Society

Synopsis

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A smoother quantum measurement

Published 15 March 2010

A method called quantum smoothing has been experimentally shown to provide a mean-square measurement error that is a factor of 2 smaller than the quantum limit.

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Authors & Affiliations

T. A. Wheatley1,2,3, D. W. Berry4, H. Yonezawa3, D. Nakane3, H. Arao3, D. T. Pope5, T. C. Ralph1,6,*, H. M. Wiseman1,7,†, A. Furusawa3,‡, and E. H. Huntington1,2,§

  • 1Centre for Quantum Computer Technology, Australian Research Council
  • 2School of Engineering and Information Technology, University College, The University of New South Wales, Canberra 2600, ACT, Australia
  • 3Department of Applied Physics and Quantum Phase Electronics Center, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
  • 4Institute for Quantum Computing, University of Waterloo, Waterloo, ON, Canada
  • 5Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo, ON N2L 2Y5, Canada
  • 6Department of Physics, University of Queensland, Brisbane 4072, QLD, Australia
  • 7Centre for Quantum Dynamics, Griffith University, Brisbane 4111, QLD, Australia

  • *ralph@physics.uq.edu.au
  • h.wiseman@griffith.edu.au
  • akiraf@ap.t.u-tokyo.ac.jp
  • §e.huntington@adfa.edu.au

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Issue

Vol. 104, Iss. 9 — 5 March 2010

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