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Proceedings Paper

Fundamental precision limit of an interferometric sensor when one of the inputs is the vacuum (Conference Presentation)
Author(s): Masahiro Takeoka; Kaushik P. Seshadreesan; Chenglong You; Shuro Izumi; Jonathan P. Dowling
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Paper Abstract

In the lore of quantum metrology, one often hears (or reads) the following no-go theorem: If you put a vacuum into one input port of a balanced Mach-Zehnder interferometer, then no matter what you put into the other input port, and no matter what your detection scheme, the sensitivity can never be better than the shot-noise limit (SNL). Often the proof of this theorem is cited to be in C. Caves, Phys. Rev. D 23, 1693 (1981), but upon further inspection, no such claim is made there. Quantum-Fisher-information-based arguments suggestive of this no-go theorem appear elsewhere in the literature, but are not stated in their full generality. Here we thoroughly explore this no-go theorem and give a rigorous statement: the no-go theorem holds whenever the unknown phase shift is split between both of the arms of the interferometer, but remarkably does not hold when only one arm has the unknown phase shift. In the latter scenario, we provide an explicit measurement strategy that beats the SNL. We also point out that these two scenarios are physically different and correspond to different types of sensing applications.

Paper Details

Date Published: 6 November 2018
Proc. SPIE 10771, Quantum Communications and Quantum Imaging XVI, 1077106 (6 November 2018); doi: 10.1117/12.2320916
Show Author Affiliations
Masahiro Takeoka, National Institute of Information and Communications Technology (Japan)
Kaushik P. Seshadreesan, The Univ. of Arizona (United States)
Chenglong You, Louisiana State Univ. (United States)
Shuro Izumi, Technical Univ. of Denmark (Denmark)
Jonathan P. Dowling, Louisiana State Univ. (United States)

Published in SPIE Proceedings Vol. 10771:
Quantum Communications and Quantum Imaging XVI
Ronald E. Meyers; Yanhua Shih; Keith S. Deacon, Editor(s)

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