Entanglement and nonlocality in multi-particle systems

TL;DR

This paper develops experimental criteria for detecting various forms of quantum nonlocality in multi-particle systems, bridging microscopic and macroscopic regimes, with applications to spin systems, entanglement, and Bose-Einstein condensates.

Contribution

It introduces multipartite Bell inequalities and spin squeezing criteria tailored for multi-particle systems, advancing understanding of quantum nonlocality in complex states.

Findings

Derived Bell inequalities for multi-particle spin systems.

Reviewed spin squeezing inequalities for entanglement detection.

Applied criteria to GHZ states and BEC ground states.

Abstract

Entanglement, the Einstein-Podolsky-Rosen (EPR) paradox and Bell's failure of local-hidden-variable (LHV) theories are three historically famous forms of "quantum nonlocality". We give experimental criteria for these three forms of nonlocality in multi-particle systems, with the aim of better understanding the transition from microscopic to macroscopic nonlocality. We examine the nonlocality of N separated spin J systems. First, we obtain multipartite Bell inequalities that address the correlation between spin values measured at each site, and then we review spin squeezing inequalities that address the degree of reduction in the variance of collective spins. The latter have been particularly useful as a tool for investigating entanglement in Bose-Einstein condensates (BEC). We present solutions for two topical quantum states: multi-qubit Greenberger-Horne-Zeilinger (GHZ) states, and the ground state of a two-well BEC.