Adaptive measurements and optimal states for quantum interferometry

D. W. Berry, H. M. Wiseman

Research output: Chapter in Book/Report/Conference proceedingConference proceeding contributionpeer-review

1 Citation (Scopus)


Summary form only given. Interferometry is the basis of many high-precision measurements. The ultimate limit to the precision is due to quantum effects. This limit is most easily explored for a Mach-Zehnder interferometer The outputs of this device can be measured to yield an estimate φ of the phase difference φ between the two arms of the interferometer. It is well known that this can achieve the standard quantum limit for phase variance when an N-photon number state enters one input port. Several authors have proposed ways of reducing the phase variance to the Heisenberg limit. In this paper we show that there is a physical measurement scheme using photodetectors and feedback that is almost as good as the optimal measurement. The fundamental idea is that, in addition to the unknown phase we wish to measure, φ, in one arm of the interferometer, we introduce a known phase shift, Φ, into the other arm of the interferometer. After each photodetection we adjust this introduced phase shift in order to minimize the expected uncertainty of our best phase estimate φ after the next photodetection. This feedback process is uniquely defined using Bayesian statistics, and can be solved exactly for moderate photon numbers.

Original languageEnglish
Title of host publicationTechnical Digest - Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, QELS 2001
Place of PublicationPiscataway, N.J.
PublisherInstitute of Electrical and Electronics Engineers (IEEE)
Number of pages2
ISBN (Electronic)155752663X, 9781557526632
Publication statusPublished - May 2001
Externally publishedYes
EventQuantum Electronics and Laser Science Conference, QELS 2001 - Baltimore, United States
Duration: 6 May 200111 May 2001


OtherQuantum Electronics and Laser Science Conference, QELS 2001
Country/TerritoryUnited States


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