All-Versus-Nothing Violation of Local Realism by Swapping Entanglement

TL;DR

This paper demonstrates an all-versus-nothing violation of local realism through a partial entanglement swapping process, proposing a practical inequality that can be violated quantum mechanically, highlighting the nonlocal nature of entanglement swapping.

Contribution

It introduces a new inequality for entanglement swapping that can be experimentally tested to reveal nonlocality beyond previous bounds.

Findings

Quantum violation up to 4 times Cirel'son's bound

Proposed a practical experiment for testing nonlocality

Uncovered the nonlocal character of entanglement swapping

Abstract

The usual entanglement swapping protocol can entangle two particles that never interact. Here we demonstrate an all-versus-nothing violation of local realism for a partial entanglement swapping process. A Clauser-Horne-Shimony-Holt-type inequality for two particles entangled by entanglement swapping is proposed for a practical experiment and can be violated quantum mechanically up to 4 beyond Cirel'son's bound 2sqr(2). Our result uncovers the intriguing nonlocal character of entanglement swapping and may lead to a conclusive (loophole-free) test of local realism versus quantum mechanics. The experimental test of the nonlocality under current technology is also discussed.