Maximum quantum nonlocality between systems that never interacted

TL;DR

This paper demonstrates that systems which never interacted can exhibit maximal quantum nonlocality, using entanglement swapping and nonlocal boxes with specific measurement settings, challenging traditional notions of nonlocality.

Contribution

It introduces a feasible scenario with 3 measurements and 4 outputs where nonlocal boxes are possible, and shows how entanglement swapping enables nonlocal correlations without prior interaction.

Findings

Nonlocal boxes are feasible with 3 measurements and 4 outputs.

Entanglement swapping can produce nonlocal correlations between non-interacting systems.

Systems can exhibit maximal nonlocality without direct interaction.

Abstract

We show that there is a stronger form of bipartite quantum nonlocality in which systems that never interacted are as nonlocal as allowed by no-signaling. For this purpose, we first show that nonlocal boxes, theoretical objects that violate a bipartite Bell inequality as much as the no-signaling principle allows and which are physically impossible for most scenarios, are feasible if the two parties have 3 measurements with 4 outputs. Then we show that, in this case, entanglement swapping allows us to prepare mixtures of nonlocal boxes using systems that never interacted.