Dissipative versus conditional generation of Gaussian entanglement and spin squeezing
Denis V. Vasilyev, Christine A. Muschik, Klemens Hammerer · Physical Review A · 2013
Spin squeezing of collective atomic spins can be achieved conditionally via probing with light and subsequent homodyne detection, as is done in a quantum nondemolition measurement. Recently it has been shown that squeezing can also be created unconditionally by a properly designed dissipative dynamics. We compare the two approaches in a Gaussian description and optimize over all Gaussian light-matter interactions. We find that in the optimal unconditional scheme based on dissipation the level of squeezing scales with optical depth as ${d}^{\ensuremath{-}1/2}$. In contrast, the optimal conditional scheme based on measurement of light---which in fact is not a quantum nondemolition measurement---can provide squeezing which scales as ${d}^{\ensuremath{-}1}$. Our results apply directly also to the creation of entanglement in the form of nonlocal spin squeezing of two atomic ensembles.