Nonlocality of All Quantum Networks

TL;DR

This paper explores the nonlocal properties of quantum networks, demonstrating their inherent nonlocality and activated nonlocality through new theoretical methods, highlighting quantum advantages over classical networks.

Contribution

It introduces a novel approach to characterize and prove nonlocality in complex quantum networks, including activated nonlocality resulting from entanglement swapping.

Findings

Proves tripartite nonlocality in chain-shaped networks.

Establishes activated nonlocality for all bipartite entangled states.

Shows nonlocality and quantum advantage in all connected quantum networks.

Abstract

The multipartite correlations derived from local measurements on some composite quantum systems are inconsistent with those reproduced classically. This inconsistency is known as quantum nonlocality and shows a milestone in the foundations of quantum theory. Still, it is NP hard to decide a nonlocal quantum state. We investigate an extended question: how to characterize the nonlocal properties of quantum states that are distributed and measured in networks. We first prove the generic tripartite nonlocality of chain-shaped quantum networks using semiquantum nonlocal games. We then introduce a new approach to prove the generic activated nonlocality as a result of entanglement swapping for all bipartite entangled states. The result is further applied to show the multipartite nonlocality and activated nonlocality for all nontrivial quantum networks consisting of any entangled states. Our results provide the nonlocality witnesses and quantum superiorities of all connected quantum networks or nontrivial hybrid networks in contrast to classical networks.