Experimental demonstration of genuine tripartite nonlocality under strict locality conditions

TL;DR

This paper reports an experimental demonstration of genuine tripartite nonlocality in a photonic network under strict locality conditions, closing loopholes and disproving bipartite resource explanations.

Contribution

It provides the first loophole-free experimental verification of genuine tripartite nonlocality in a network with strict locality constraints.

Findings

Observed a 7.57 standard deviation violation of Bell inequality.

Achieved a high-fidelity GHZ state of 93.13%.

Disproved bipartite resource models for tripartite nonlocality.

Abstract

Nonlocality captures one of the counterintuitive features of nature that defies classical intuition. Recent investigations reveal that our physical world's nonlocality is at least tripartite; i.e., genuinely tripartite nonlocal correlations in nature cannot be reproduced by any causal theory involving bipartite nonclassical resources and unlimited shared randomness. Here, by allowing the fair sampling assumption and postselection, we experimentally demonstrate such genuine tripartite nonlocality in a network under strict locality constraints that are ensured by spacelike separating all relevant events and employing fast quantum random number generators and high-speed polarization measurements. In particular, for a photonic quantum triangular network we observe a locality-loophole-free violation of the Bell-type inequality by 7.57 standard deviations for a postselected tripartite Greenberger-Horne-Zeilinger state of fidelity $(93.13 \pm 0.24)\%$, which convincingly disproves the possibility of simulating genuine tripartite nonlocality by bipartite nonlocal resources with globally shared randomness.