Test of Genuine Multipartite Nonlocality

TL;DR

This paper introduces a Bell-type inequality to test genuine multipartite nonlocality, and experimentally demonstrates its violation using four-photon GHZ states, confirming the presence of complex nonlocal correlations in nature.

Contribution

It provides a new inequality for testing multipartite nonlocality and experimentally verifies its violation with four-photon GHZ states, advancing understanding of quantum nonlocality.

Findings

Four-photon GHZ states violate the inequality significantly.

The results confirm the existence of genuine multipartite nonlocal correlations.

The inequality tests for nonlocality beyond three-partite resources.

Abstract

While Bell nonlocality of a bipartite system is counter-intuitive, multipartite nonlocality in our many-body world turns out to be even more so. Recent theoretical study reveals in a theory-agnostic manner that genuine multipartite nonlocal correlations cannot be explained by any causal theory involving fewer-partite nonclassical resources and global shared randomness. Here we provide a Bell-type inequality as a test for genuine multipartite nonlocality in network by exploiting a matrix representation of the causal structure of a multipartite system. We further present experimental demonstrations that both four-photon GHZ state and generalized four-photon GHZ state significantly violate the inequality, i.e., the observed four-partite correlations resist explanations involving three-way nonlocal resources subject to local operations and common shared randomenss, hence confirming that nature is boundless multipartite nonlocal.