Dipartimento di Fisica - Sapienza Università di Roma, P.le Aldo Moro 5, I-00185 Roma, Italy.
International Institute of Physics, Federal University of Rio Grande do Norte, 59070-405 Natal, Brazil.
Nat Commun. 2017 Mar 16;8:14775. 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.
贝尔定理在量子信息处理中起着至关重要的作用，因此多年来已经进行了多次违反贝尔不等式的实验研究。然而，尽管它们具有基础性的意义，但以前的实验并没有考虑到对量子网络具有重要意义的一个因素：即远距离各方之间的相关性是由多个、通常是独立的源介导的。在这里，我们使用光子设备研究了一个由三个空间分离的节点组成的量子网络，其相关性由两个不同的源介导。这种情况允许出现所谓的非双局域相关性，与任何涉及两个独立隐藏变量的局部模型都不兼容。我们通过在公平抽样假设下违反类似贝尔的不等式，实验性地见证了这种量子相关性的出现。我们的结果为网络中贝尔定理的推广提供了一个原理性实验证明，这可能是量子通信协议的潜在资源。
