Experimental full network nonlocality with independent sources and strict locality constraints

TL;DR

This paper reports an experiment demonstrating full network nonlocality with independent sources, closing key loopholes and violating classical inequalities by over five standard deviations, thus certifying non-classical sources in a network.

Contribution

The authors experimentally demonstrate full network nonlocality with independent sources while closing major loopholes, advancing the understanding of quantum correlations in complex networks.

Findings

Violation of non-full network nonlocality inequalities by over five standard deviations

Certification of the absence of classical sources in the network

Closure of source-independence, locality, and measurement-independence loopholes

Abstract

Nonlocality arising in networks composed of several independent sources gives rise to phenomena radically different from that in standard Bell scenarios. Over the years, the phenomenon of network nonlocality in the entanglement-swapping scenario has been well investigated and demonstrated. However, it is known that violations of the so-called bilocality inequality used in previous experimental demonstrations cannot be used to certify the non-classicality of their sources. This has put forward a stronger concept for nonlocality in networks, called full network nonlocality. Here, we experimentally observe full network nonlocal correlations in a network where the source-independence, locality, and measurement-independence loopholes are closed. This is ensured by employing two independent sources, rapid setting generation, and space-like separations of relevant events. Our experiment violates known inequalities characterizing non-full network nonlocal correlations by over five standard deviations, certifying the absence of classical sources in the realization.