Phys. Rev. Lett. 105, 093602 (2010) [4 pages]Quantum Nondemolition Measurement of Large-Spin Ensembles by Dynamical DecouplingReceived 17 May 2010; revised 26 July 2010; published 25 August 2010 Quantum nondemolition (QND) measurement of collective variables by off-resonant optical probing has the ability to create entanglement and squeezing in atomic ensembles. Until now, this technique has been applied to real or effective spin one-half systems. We show theoretically that the buildup of Raman coherence prevents the naive application of this technique to larger spin atoms, but that dynamical decoupling can be used to recover the ideal QND behavior. We experimentally demonstrate dynamical decoupling by using a two-polarization probing technique. The decoupled QND measurement achieves a sensitivity 5.7(6) dB better than the spin projection noise. © 2010 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.105.093602
DOI:
10.1103/PhysRevLett.105.093602
PACS:
42.50.Lc, 03.67.Bg, 07.55.Ge, 42.50.Dv
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