title: Experimental violation of local causality in a quantum network.
abstract: 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.
authors.affiliation: Dipartimento di Fisica - Sapienza Università di Roma, P.le Aldo Moro 5, I-00185 Roma, Italy.
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Carvacho
authors.affiliation: Dipartimento di Fisica - Sapienza Università di Roma, P.le Aldo Moro 5, I-00185 Roma, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Andreoli
authors.affiliation: Dipartimento di Fisica - Sapienza Università di Roma, P.le Aldo Moro 5, I-00185 Roma, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Santodonato
authors.affiliation: Dipartimento di Fisica - Sapienza Università di Roma, P.le Aldo Moro 5, I-00185 Roma, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Bentivegna
authors.affiliation: International Institute of Physics, Federal University of Rio Grande do Norte, 59070-405 Natal, Brazil.|Institute for Theoretical Physics, University of Cologne, 50937 Cologne, Germany.
authors.forename: Rafael
authors.initials: R
authors.lastname: Chaves
authors.affiliation: Dipartimento di Fisica - Sapienza Università di Roma, P.le Aldo Moro 5, I-00185 Roma, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Sciarrino