Experimental non-locality in a quantum network

TL;DR

This paper experimentally demonstrates a new form of quantum non-locality in a network with multiple independent sources, violating a novel Bell inequality, and advancing quantum communication understanding.

Contribution

It presents the first experimental verification of generalized Bell inequalities in a quantum network with independent sources.

Findings

Violation of a new Bell inequality in a three-node quantum network

Experimental evidence of non-local correlations mediated by independent sources

First proof-of-principle for generalized Bell's theorem in networks

Abstract

Non-locality stands nowadays not only as one of the cornerstones of quantum theory, but also plays a crucial role in quantum information processing. Several experimental investigations of nonlocality have been carried out over the years. In spite of their fundamental relevance, however, all previous experiments do not consider a crucial ingredient that is ubiquitous in quantum networks: the fact that correlations between distant parties are mediated by several, typically independent, sources of quantum states. Here, using a photonic setup we investigate a quantum network consisting of three spatially separated nodes whose correlations are mediated by two independent sources. This scenario allows for the emergence of a new kind of non-local correlations that we experimentally witness by violating a novel Bell inequality. Our results provide the first experimental proof-of-principle of generalizations of Bell's theorem for networks, a topic that has attracted growing attention and promises a novel route for quantum communication protocols.