Adaptive quantum measurements of a continuously varying phase.

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Title Adaptive quantum measurements of a continuously varying phase.
Author Berry, D.W.; Wiseman, Howard Mark
Journal Name Physical Review A: Atomic, Molecular and Optical Physics
Year Published 2002
Place of publication USA
Publisher American Physical Society
Abstract We analyze the problem of quantum-limited estimation of a stochastically varying phase of a continuous beam (rather than a pulse) of the electromagnetic field. We consider both nonadaptive and adaptive measurements, and both dyne detection (using a local oscillator) and interferometric detection. We take the phase variation to be φ̇=sqrt[κ]ξ(t), where ξ(t) is δ-correlated Gaussian noise. For a beam of power P, the important dimensionless parameter is N=P/ħωκ, the number of photons per coherence time. For the case of dyne detection, both continuous-wave (cw) coherent beams and cw (broadband) squeezed beams are considered. For a coherent beam a simple feedback scheme gives good results, with a phase variance ≃N-1/2/2. This is sqrt[2] times smaller than that achievable by nonadaptive (heterodyne) detection. For a squeezed beam a more accurate feedback scheme gives a variance scaling as N-2/3, compared to N-1/2 for heterodyne detection. For the case of interferometry only a coherent input into one port is considered. The locally optimal feedback scheme is identified, and it is shown to give a variance scaling as N-1/2. It offers a significant improvement over nonadaptive interferometry only for N of order unity.
Peer Reviewed Yes
Published Yes
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Copyright Statement Copyright 2002 American Physical Society. This is the author-manuscript version of this paper. Reproduced in accordance with the copyright policy of the publisher. Please refer to the journal's website for access to the definitive, published version.
Volume 65
Page from 043803.1
Page to 043803.11
ISSN 1050-2947
Date Accessioned 2003-04-11
Language en_AU
Research Centre Centre for Quantum Dynamics
Faculty Faculty of Science
Subject PRE2009-Theoretical Physics
Publication Type Journal Articles (Refereed Article)
Publication Type Code c1

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