Quantum networks play a crucial role in distributed quantum information processing, enabling the establishment of entanglement and quantum communication among distant nodes. Fundamentally, networks with independent sources allow for new forms of nonlocality, beyond the paradigmatic Bell’s theorem. Here we implement the simplest of such networks—the bilocality scenario—in an urban network connecting different buildings with a fully scalable and hybrid approach. Two independent sources using different technologies—a quantum dot and a nonlinear crystal—are used to share a photonic entangled state among three nodes connected through a 270 m free-space channel and fiber links. By violating a suitable nonlinear Bell inequality, we demonstrate the nonlocal behavior of the correlations among the nodes of the network. Our results pave the way towards the realization of more complex networks and the implementation of quantum communication protocols in an urban environment, leveraging the capabilities of hybrid photonic technologies.

中文翻译：

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使用混合光子技术在城市网络中对局部因果关系的量子破坏

量子网络在分布式量子信息处理中发挥着至关重要的作用，能够在远距离节点之间建立纠缠和量子通信。从根本上说，具有独立来源的网络允许新形式的非局域性，超出范式贝尔定理。在这里，我们在连接不同建筑物的城市网络中实现了最简单的此类网络——双向场景——采用完全可扩展和混合的方法。使用不同技术的两个独立源——量子点和非线性晶体——用于在通过 270 m 自由空间通道和光纤链路连接的三个节点之间共享光子纠缠态。通过违反合适的非线性贝尔不等式，我们证明了网络节点之间相关性的非局部行为。