Optimal states and almost optimal adaptive measurements for quantum interferometry

D. W. Berry*, H. M. Wiseman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

180 Citations (Scopus)


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)2 ≃ π2/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.

Original languageEnglish
Pages (from-to)5098-5101
Number of pages4
JournalPhysical Review Letters
Issue number24
Publication statusPublished - 11 Dec 2000
Externally publishedYes


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