Bell Correlations in a Bose-Einstein Condensate

TL;DR

This paper demonstrates the detection of Bell correlations in a Bose-Einstein condensate of around 480 atoms, showing that strong non-classical correlations can be observed in many-body quantum systems through collective measurements.

Contribution

The authors derive a Bell correlation witness for many-particle systems and experimentally observe Bell correlations exceeding classical thresholds in a spin-squeezed Bose-Einstein condensate.

Findings

Bell correlations detected in a 480-atom condensate

Measurement exceeds Bell correlation threshold by 3.8 standard deviations

Shows non-classical correlations are accessible in many-body systems

Abstract

Characterizing many-body systems through the quantum correlations between their constituent particles is a major goal of quantum physics. Although entanglement is routinely observed in many systems, we report here the detection of stronger correlations - Bell correlations - between the spins of about 480 atoms in a Bose-Einstein condensate. We derive a Bell correlation witness from a many-particle Bell inequality involving only one- and two-body correlation functions. Our measurement on a spin-squeezed state exceeds the threshold for Bell correlations by 3.8 standard deviations. Our work shows that the strongest possible non-classical correlations are experimentally accessible in many-body systems, and that they can be revealed by collective measurements.