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arXiv · 0912.1162

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·E. H. Huntington
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Abstract

Quantum parameter estimation has many applications, from gravitational wave detection to quantum key distribution. We present the first experimental demonstration of the time-symmetric technique of quantum smoothing. We consider both adaptive and non-adaptive quantum smoothing, and show that both are better than their well-known time-asymmetric counterparts (quantum filtering). 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 $2\sqrt{2}$ times smaller than that from non-adaptive quantum filtering (the standard quantum limit). The experimentally measured improvement is $2.24 \pm 0.14$.

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T. A. Wheatley, D. W. Berry, H. Yonezawa, D. Nakane, H. Arao, D. T. Pope, T. C. Ralph, H. M. Wiseman, A. Furusawa, E. H. Huntington. 2009-12-07. Adaptive Optical Phase Estimation Using Time-Symmetric Quantum Smoothing. https://doi.org/10.1103/physrevlett.104.093601

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