Revealing Genuine Optical-Path Entanglement

TL;DR

This paper proposes a scalable, assumption-free protocol for detecting genuine multipartite optical-path entanglement using local measurements, with demonstrated experiments showing robustness to loss and potential for quantum network certification.

Contribution

It introduces a novel entanglement witness protocol that does not rely on post-selection or photon number assumptions, enabling scalable and robust detection of multipartite entanglement.

Findings

Protocol successfully detects entanglement in two and three optical paths.

The method is scalable and resistant to loss.

It guarantees entanglement in a single-photon subspace.

Abstract

How can one detect entanglement between multiple optical paths sharing a single photon? We address this question by proposing a scalable protocol, which only uses local measurements where single photon detection is combined with small displacement operations. The resulting entanglement witness does not require post-selection, nor assumptions about the photon number in each path. Furthermore, it guarantees that entanglement lies in a subspace with at most one photon per optical path and reveals genuinely multipartite entanglement. We demonstrate its scalability and resistance to loss by performing various experiments with two and three optical paths. We anticipate applications of our results for quantum network certification.