Device-independent and semi-device-independent entanglement certification in broadcast Bell scenarios

TL;DR

This paper advances the understanding of entanglement certification and Bell nonlocality activation through broadcasting, demonstrating new Bell inequalities, tripartite nonlocal correlations, and device-independent certification for Werner states.

Contribution

It introduces tailored Bell inequalities for broadcast scenarios, shows activation of tripartite nonlocality from local models, and proves device-independent certification for Werner states.

Findings

Broadcasting can activate Bell nonlocality beyond previous bounds.

Device-independent certification of Werner states is possible in most entanglement ranges.

Activation of EPR steering demonstrated in broadcast scenarios.

Abstract

It has recently been shown that by broadcasting the subsystems of a bipartite quantum state, one can activate Bell nonlocality and significantly improve noise tolerance bounds for device-independent entanglement certification. In this work we strengthen these results and explore new aspects of this phenomenon. First, we prove new results related to the activation of Bell nonlocality. We construct Bell inequalities tailored to the broadcast scenario, and show how broadcasting can lead to even stronger notions of Bell nonlocality activation. In particular, we exploit these ideas to show that bipartite states admitting a local hidden-variable model for general measurements can lead to genuine tripartite nonlocal correlations. We then study device-independent entanglement certification in the broadcast scenario, and show through semidefinite programming techniques that device-independent entanglement certification is possible for the two-qubit Werner state in essentially the entire range of entanglement. Finally, we extend the concept of EPR steering to the broadcast scenario, and present novel examples of activation of the two-qubit isotropic state. Our results pave the way for broadcast-based device-dependent and semi-device-independent protocols.