Quantum spin squeezing

TL;DR

This review paper discusses the concept of quantum spin squeezing, its theoretical foundations, generation methods, relation to entanglement and quantum Fisher information, and various applications including quantum metrology, chaos detection, and experimental realizations.

Contribution

It provides a comprehensive overview of quantum spin squeezing, covering definitions, properties, generation techniques, and applications, integrating recent experimental and theoretical developments.

Findings

Spin squeezing relates to entanglement and enhances measurement precision.

Various methods to produce spin-squeezed states include Ising and nonlinear Hamiltonians.

Spin squeezing is useful for detecting quantum chaos and phase transitions.

Abstract

This paper reviews quantum spin squeezing, which characterizes the sensitivity of a state with respect to an SU(2) rotation, and is significant for both entanglement detection and high-precision metrology. We first present various definitions of spin squeezing parameters, explain their origin and properties for typical states, and then discuss spin-squeezed states produced with the Ising and the nonlinear twisting Hamiltonians. Afterwards, we explain correlations and entanglement in spin-squeezed states, as well as the relations between spin squeezing and quantum Fisher information, where the latter plays a central role in quantum metrology. We also review the applications of spin squeezing for detecting quantum chaos and quantum phase transitions, as well as the influence of decoherence on spin-squeezed states. Finally, several experiments are discussed including: producing spin squeezed states via particle collisions in Bose-Einstein condensates, mapping photon squeezing onto atomic ensembles, and quantum non-demolition measurements.