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Optimal states and almost optimal adaptive measurements for quantum interferometry

D. W. Berry·H. M. Wiseman
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Abstract

We derive the optimal N-photon two-mode input state for obtaining an estimate ϕof 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)^2 \simeq π^2/N^2, 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 ϕvery close to that from an optimal measurement.

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D. W. Berry, H. M. Wiseman. 2002-09-18. Optimal states and almost optimal adaptive measurements for quantum interferometry. https://doi.org/10.1103/physrevlett.85.5098

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