All Entangled States are Nonlocal and Self-Testable in the Broadcast Scenario

TL;DR

This paper demonstrates that in a broadcast scenario, all entangled states exhibit nonlocality and can be self-tested, bridging the gap between entanglement and Bell nonlocality.

Contribution

It proves that all entangled states are broadcast nonlocal and introduces a method for self-testing multipartite states within this framework.

Findings

All entangled states are broadcast nonlocal.

Multipartite states can be broadcast-self-tested.

The results unify entanglement and nonlocality in the broadcast scenario.

Abstract

Entanglement and Bell nonlocality are known to be inequivalent: there exist entangled states that admit a local hidden-variable model for all local measurements. Here we show that this gap disappears in a minimal broadcast extension of the Bell scenario. Assuming only the validity of quantum theory, we prove that for every entangled state $\rho_{AB}$ there exist local broadcasting maps and local measurements such that the resulting four--partite correlations cannot be reproduced by any broadcast network whose source is separable across the $A|B$ cut. Thus, all entangled states are broadcast nonlocal in quantum theory. In addition, we show that all (also mixed) multipartite states can be broadcast-self-tested, according to a natural operational definition.