Unitary cavity spin squeezing by quantum erasure

Deterministic light-induced spin squeezing in an atomic gas is limited by photon shot noise or, equivalently, by atomic state information escaping with the light field mediating the effective atom-atom interaction. We show theoretically that the performance of cavity spin squeezing [ M. H. Schleier-Smith, I. D. Leroux and V. Vuletić Phys. Rev. A 81 021804 (2010)] can be substantially improved by erasing the light-atom entanglement, and propose several methods for doing so. Accounting for light scattering into free space, quantum erasure improves the scaling of cavity squeezing from S[superscript −1/2] to S[superscript −2/3], where S is the total atomic spin.Natural Sciences and Engineering Research Council of Canada (NSERC)Hertz FoundationNational Science Foundation (U.S.)United States. Defense Advanced Research Projects AgencyUnited States. Army Research Offic