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arXiv · 1310.3177

Reduced back-action for phase sensitivity 10 times beyond the standard quantum limit

Justin G. Bohnet·Kevin C. Cox·Matthew A. Norcia·Joshua M. Weiner·Zilong Chen·James K. Thompson
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Abstract

Collective measurements can project a system into an entangled state with enhanced sensitivity for measuring a quantum phase, but measurement back-action has limited previous efforts to only modest improvements. Here we use a collective measurement to produce and directly observe, with no background subtraction, an entangled, spin-squeezed state with phase resolution improved in variance by a factor of 10.5(1.5), or 10.2(6) dB, compared to the initially unentangled ensemble of N = 4.8 x 10^5 87Rb atoms. The measurement uses a cavity-enhanced probe of an optical cycling transition to mitigate back-action associated with state-changing transitions induced by the probe. This work establishes collective measurements as a powerful technique for generating entanglement for precision measurement, with potential impacts in biological sensing, communication, navigation, and tests of fundamental physics.

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Justin G. Bohnet, Kevin C. Cox, Matthew A. Norcia, Joshua M. Weiner, Zilong Chen, James K. Thompson. 2013-10-11. Reduced back-action for phase sensitivity 10 times beyond the standard quantum limit. https://doi.org/10.1038/nphoton.2014.151

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