Characterizing the nonlocal correlations of particles that never interacted

TL;DR

This paper demonstrates that entanglement swapping can produce nonlocal correlations between particles that never directly interacted, showing Bell inequality violations at lower visibilities than traditional methods.

Contribution

It introduces local models for uncorrelated quantum systems and shows that entanglement swapping enables Bell inequality violations at lower visibilities.

Findings

Bell inequality violated at 50% visibility with entanglement swapping

Traditional entangled pairs require 70% visibility to violate Bell inequalities

Entanglement swapping enhances nonlocal correlations in non-interacting particles

Abstract

Quantum systems that have never interacted can become nonlocally correlated through a process called entanglement swapping. To characterize nonlocality in this context, we introduce local models where quantum systems that are initially uncorrelated are described by uncorrelated local variables. While a pair of maximally entangled qubits prepared in the usual way (i.e., emitted from a common source) requires a visibility close to 70% to violate a Bell inequality, we show that an entangled pair generated through entanglement swapping will already violate a Bell inequality for visibilities as low as 50% under our assumption.