Spin squeezing, entanglement and quantum metrology with Bose-Einstein condensates

TL;DR

This paper reviews the generation and detection of spin squeezing in Bose-Einstein condensates, highlighting experimental methods and results that enhance quantum metrology capabilities.

Contribution

It provides a comprehensive overview of spin squeezing techniques in atomic systems, including experimental implementations in Bose-Einstein condensates.

Findings

Demonstrated adiabatic spin squeezing using motional degrees of freedom.

Achieved diabatic spin squeezing based on hyperfine states.

Outlined experimental requirements for coherent spin squeezing detection.

Abstract

Squeezed states, a special kind of entangled states, are known as a useful resource for quantum metrology. In interferometric sensors they allow to overcome the "classical" projection noise limit stemming from the independent nature of the individual photons or atoms within the interferometer. Motivated by the potential impact on metrology as wells as by fundamental questions in the context of entanglement, a lot of theoretical and experimental effort has been made to study squeezed states. The first squeezed states useful for quantum enhanced metrology have been proposed and generated in quantum optics, where the squeezed variables are the coherences of the light field. In this tutorial we focus on spin squeezing in atomic systems. We give an introduction to its concepts and discuss its generation in Bose-Einstein condensates. We discuss in detail the experimental requirements necessary for the generation and direct detection of coherent spin squeezing. Two exemplary experiments demonstrating adiabatically prepared spin squeezing based on motional degrees of freedom and diabatically realized spin squeezing based on internal hyperfine degrees of freedom are discussed.