Mesoscopic atomic entanglement for precision measurements beyond the standard quantum limit
- Danish National Research Foundation Center for Quantum Optics, The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark
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Edited by H. Jeffrey Kimble, California Institute of Technology, Pasadena, CA, and approved April 30, 2009 (received for review February 11, 2009)
Abstract
Squeezing of quantum fluctuations by means of entanglement is a well-recognized goal in the field of quantum information science and precision measurements. In particular, squeezing the fluctuations via entanglement between 2-level atoms can improve the precision of sensing, clocks, metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically relevant squeezing and entanglement for ≳ 105 cold caesium atoms via a quantum nondemolition (QND) measurement on the atom clock levels. We show that there is an optimal degree of decoherence induced by the quantum measurement which maximizes the generated entanglement. A 2-color QND scheme used in this paper is shown to have a number of advantages for entanglement generation as compared with a single-color QND measurement.
Footnotes
- 1To whom correspondence should be addressed. E-mail: polzik{at}nbi.dk
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Author contributions: J.A., P.J.W., D.O., U.B.H., N.K., and E.S.P. designed research; J.A., P.J.W., D.O., U.B.H., N.K., and E.S.P. performed research; and J.A., N.K., and E.S.P. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0901550106/DCSupplemental.
