Bilocal Bell inequalities violated by the quantum Elegant Joint Measurement

TL;DR

This paper explores bilocal Bell inequalities in quantum networks, introducing a family of symmetric measurements that reveal noise-tolerant quantum correlations beyond traditional Bell nonlocality, and proposes an experimental implementation.

Contribution

It introduces a new family of symmetric iso-entangled measurements generalizing the Elegant Joint Measurement, leading to noise-tolerant quantum correlations and novel network Bell inequalities.

Findings

Quantum correlations violate bilocal inequalities under noise.

New symmetric measurement bases enable nonlocality beyond standard Bell tests.

Proposed quantum circuit facilitates experimental realization of the measurements.

Abstract

Network Bell experiments give rise to a form of quantum nonlocality that conceptually goes beyond Bell's theorem. We investigate here the simplest network, known as the bilocality scenario. We depart from the typical use of the Bell State Measurement in the network central node and instead introduce a family of symmetric iso-entangled measurement bases that generalise the so-called Elegant Joint Measurement. This leads us to report noise-tolerant quantum correlations that elude bilocal variable models. Inspired by these quantum correlations, we introduce network Bell inequalities for the bilocality scenario and show that they admit noise-tolerant quantum violations. In contrast to many previous studies of network Bell inequalities, neither our inequalities nor their quantum violations are based on standard Bell inequalities and standard quantum nonlocality. Moreover, we pave the way for an experimental realisation by presenting a simple two-qubit quantum circuit for the implementation of the Elegant Joint Measurement and our generalisation.