Nonlocality activation in entanglement swapping chains

TL;DR

This paper investigates how entanglement swapping chains can activate nonlocal correlations, specifically CHSH inequality violations, in states that initially do not violate it, revealing state-dependent critical points for nonlocality activation.

Contribution

It demonstrates that entanglement swapping can activate nonlocality in initially local states and identifies state-dependent critical numbers for this activation.

Findings

Activation of CHSH violation depends on the number of entanglement swappings.

Different initial states have different critical numbers for nonlocality activation.

Nonlocality can be activated after multiple entanglement swappings even if initial states do not violate CHSH inequality.

Abstract

We consider multiple entanglement swappings performed on a chain of bipartite states. Each state does not violate CHSH inequality. We show that before some critical number of entanglement swappings is achieved the output state does not violate this inequality either. However, if this number is achieved then for some results of Bell measurements obtained in the protocol of entanglement swapping the output state violates CHSH inequality. Moreover, we show that for different states we have different critical numbers for which CHSH inequality is activated.