Local and scalable detection of genuine multipartite single-photon path entanglement

TL;DR

This paper introduces a scalable, local measurement-based entanglement witness for genuine multipartite single-photon path entanglement, demonstrated experimentally for 4- and 8-partite states, facilitating high-rate quantum network applications.

Contribution

The paper presents a novel, efficient entanglement witness using local measurements and displacement operations applicable to any number of parties, with experimental validation for multipartite states.

Findings

Successfully tested for 4- and 8-partite states

Witness is scalable and requires only two measurement settings

Enables high-rate distribution of photonic entanglement in networks

Abstract

How can a multipartite single-photon path-entangled state be certified efficiently by means of local measurements? We address this question by constructing an entanglement witness based on local photon detections preceded by displacement operations to reveal genuine multipartite entanglement. Our witness is defined as a sum of three observables that can be measured locally and assessed with two measurement settings for any number of parties $N$. For any bipartition, the maximum mean value of the witness observable over biseparable states is bounded by the maximum eigenvalue of an $N\times N$ matrix, which can be computed efficiently. We demonstrate the applicability of our scheme by experimentally testing the witness for heralded 4- and 8-partite single-photon path-entangled states. Our implementation shows the scalability of our witness and opens the door for distributing photonic multipartite entanglement in quantum networks at high rates.