Experimental violation of local causality in a quantum network

• Published in: Nature communications 2017-03, Vol.8 (1), p.14775-14775, Article 14775
• Main Authors: Carvacho, Gonzalo, Andreoli, Francesco, Santodonato, Luca, Bentivegna, Marco, Chaves, Rafael, Sciarrino, Fabio
• Format: Article
• Language: English
• Subjects: 639/624/400/482; 639/766/483/1139; 639/766/483/3925; Causality; Humanities and Social Sciences; multidisciplinary; Random variables; Realism; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms14775

Bell’s theorem plays a crucial role in quantum information processing and thus several experimental investigations of Bell inequalities violations have been carried out over the years. Despite their fundamental relevance, however, previous experiments did not consider an ingredient of relevance for quantum networks: the fact that correlations between distant parties are mediated by several, typically independent sources. Here, using a photonic setup, we investigate a quantum network consisting of three spatially separated nodes whose correlations are mediated by two distinct sources. This scenario allows for the emergence of the so-called non-bilocal correlations, incompatible with any local model involving two independent hidden variables. We experimentally witness the emergence of this kind of quantum correlations by violating a Bell-like inequality under the fair-sampling assumption. Our results provide a proof-of-principle experiment of generalizations of Bell’s theorem for networks, which could represent a potential resource for quantum communication protocols. Bell’s theorem has important implications for quantum information processing. Here the authors experimentally investigate the violation of a Bell-like inequality in the case of distant parties whose correlations are mediated by independent sources, a realistic feature in future quantum networks.