Dissipative versus Conditional Generation of Gaussian Entanglement and Spin Squeezing

TL;DR

This paper compares dissipative and measurement-based conditional methods for generating Gaussian spin squeezing and entanglement, showing that measurement-based schemes can achieve better scaling in certain regimes.

Contribution

It provides a detailed Gaussian analysis and optimization of both approaches, revealing the superior scaling of conditional measurement-based squeezing over dissipative methods.

Findings

Unconditional dissipative squeezing scales as d^{-1/2}.

Conditional measurement-based squeezing scales as d^{-1} in moderate optical depths.

Results extend to non-local spin squeezing of atomic ensembles.

Abstract

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 as $d^{-1/2}$. 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 $d^{-1}$ in the most relevant regime of moderate optical depths. Our results apply directly also to the creation of entanglement in the form of non-local spin squeezing of two atomic ensembles.