Optimal States and Almost Optimal Adaptive Measurements for Quantum Interferometry

Phys. Rev. Lett. 85, 5098 – Published 11 December 2000
D. W. Berry and H. M. Wiseman

Abstract

We derive the optimal N-photon two-mode input state for obtaining an estimate φ of the phase difference between two arms of an interferometer. For an optimal measurement [B. C. Sanders and G. J. Milburn, Phys. Rev. Lett. 75, 2944 (1995)], it yields a variance (Δφ)2π2/N2, compared to O(N-1) or O(N-1/2) for states considered by previous authors. Such a measurement cannot be realized by counting photons in the interferometer outputs. However, we introduce an adaptive measurement scheme that can be thus realized, and show that it yields a variance in φ very close to that from an optimal measurement.

DOI: http://dx.doi.org/10.1103/PhysRevLett.85.5098

  • Received 19 June 2000
  • Published in the issue dated 11 December 2000

© 2000 The American Physical Society

Authors & Affiliations

D. W. Berry1 and H. M. Wiseman2

  • 1Department of Physics, The University of Queensland, St. Lucia 4072, Australia
  • 2School of Science, Griffith University, Nathan, Brisbane, Queensland 4111, Australia

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