Event-Ready Bell Test Using Entangled Atoms Simultaneously Closing Detection and Locality Loopholes

Understand

An experimental test of Bell's inequality allows ruling out any local-realistic description of nature by measuring correlations between distant systems.

• While such tests are conceptually simple, there are strict requirements concerning the detection efficiency of the involved measurements, as well as the enforcement of spacelike separation between the measurement events.
• Only very recently could both loopholes be closed simultaneously.
• Here we present a statistically significant, event-ready Bell test based on combining heralded entanglement of atoms separated by $398\,\mathrm{m}$ with fast and efficient measurements of the atomic spin states closing essential loopholes.