Entanglement verification and steering when Alice and Bob cannot be trusted

TL;DR

This paper demonstrates that entanglement verification and steering can be achieved without trusting the observers by using appropriate classical and quantum communication channels, simplifying experimental tests of quantum nonlocality.

Contribution

It introduces trust-free protocols for verifying entanglement, Bell nonlocality, and EPR-steering using specific classical and quantum communication channels, extending previous work.

Findings

Trust-free verification of Bell nonlocality, EPR-steering, and entanglement.

Use of classical and quantum channels to prevent mimicking of entanglement.

Simplifies experimental demonstrations of quantum nonlocality.

Abstract

Various protocols exist by which a referee can be convinced that two observers share an entangled resource. Such protocols typically specify the types of communication allowed, and the degrees of trust required, between the referee and each observer. Here it is shown that the need for any degree of trust of the observers by the referee can be completely removed via the referee using classical and quantum communication channels appropriately. In particular, trust-free verification of Bell nonlocality, EPR-steering, and entanglement, respectively, requires two classical channels, one classical and one quantum channel, and two quantum channels. These channels correspond to suitable inputs of quantum randomness by the referee, which prevent the observers from mimicking entanglement using shared classical randomness. Our results generalize recent work by Buscemi [Phys. Rev. Lett. 108, 200401 (2012)], and offer a perspective on the operational significance of that work. They also offer the possibility of simpler experimental demonstrations of the basic idea of quantum-refereed nonlocality tests.