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Research in Optical Sciences

Spin cooling via incoherent feedback in an ensemble of cold 87Rb atoms

N. Behbood, Giorgio Colangelo, Ferran Martin Ciurana, M. Napolitano, R. J. Sewell, Morgan W. Mitchell

Published Jan 1, 2014• 0 citations
Publisher

Abstract

We report an experimental study of a new technique for spin cooling an ensemble of ultracold atoms via quantum non-demolition (QND) measurement and incoherent feedback. We have demonstrated 12db spin noise reduction. This technique has direct application in generating highly entangled macroscopic singlet state.
DOI
10.1364/qim.2014.qw4b.1

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We apply entropy removal by measurement and feedback to a cold atomic spin ensemble. Using quantum nondemolition probing by Faraday rotation measurement, and feedback by weak optical pumping, we drive the initially random collective spin variable F toward the origin F=0. We use input-output relations and ensemble quantum noise models to describe this quantum control process and identify an optimal two-round control procedure. We observe 12 dB of spin noise reduction, or a factor-of-63 reduction in phase-space volume. The method offers a nonthermal route to generation of exotic entangled states in ultracold gases, including macroscopic singlet states and strongly correlated states of quantum lattice gases.