Single-photon nonlocality in quantum networks

TL;DR

This paper demonstrates that single-photon entangled states can exhibit nonlocal correlations in a quantum network using only beamsplitters and photodetectors, expanding the understanding of nonlocality in quantum optics.

Contribution

It introduces a novel network protocol revealing nonlocality of single-photon entangled states without measurement choices, using a triangle network configuration.

Findings

Nonlocality can be demonstrated with a triangle network of three entangled states.

The protocol is robust against standard noise sources.

It offers a new approach for generating network-nonlocal correlations for quantum information.

Abstract

The state obtained when a single photon impinges on a balanced beamsplitter is often known as single-photon entangled and its nonlocal properties have been the subject of intense debates in the quantum optics and foundations communities. It is however clear that a standard Bell test made only of passive optical elements cannot reveal the nonlocality of this state. We show that the nonlocality of single-photon entangled states can nevertheless be revealed in a quantum network made only of beamsplitters and photodetectors. In our protocol, three single-photon entangled states are distributed in a triangle network, introducing indeterminacy in the photons' paths and creating nonlocal correlations without the need for measurements choices. We discuss a concrete experimental realisation and provide numerical evidence of the tolerance of our protocol to standard noise sources. Our results show that single-photon entanglement may constitute a promising solution to generate genuine network-nonlocal correlations useful for Bell-based quantum information protocols.