Quantum violation of local causality in urban network with hybrid photonic technologies

TL;DR

This paper demonstrates quantum nonlocality in an urban network using hybrid photonic technologies, showing the violation of a Bell inequality with independent sources over a 270-meter distance, advancing quantum communication infrastructure.

Contribution

First implementation of a bilocality quantum network in an urban setting using hybrid photonic sources, combining quantum dot and nonlinear crystal technologies.

Findings

Violation of a non-linear Bell inequality confirms nonlocal correlations.

Successful integration of quantum dot and nonlinear crystal sources in urban network.

Scalable approach for future complex quantum networks in city environments.

Abstract

Quantum networks play a crucial role for 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, respectively a quantum dot and a nonlinear crystal, are used to share photonic entangled state among three nodes connected through a 270 m free-space channel and fiber links. By violating a suitable non-linear Bell inequality, we demonstrate the nonlocal behaviour 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 on the capabilities of hybrid photonic technologies.