Demonstration of Quantum Nonlocality in presence of Measurement Dependence

TL;DR

This paper experimentally demonstrates quantum nonlocality under relaxed measurement independence assumptions, showing that Bell inequality violations can still be observed even when measurement settings are partially influenced by the source or an adversary.

Contribution

The study experimentally tests and confirms quantum nonlocality with limited measurement dependence, extending the validity of Bell inequality violations under more realistic conditions.

Findings

Violation of a Bell-like inequality with 99% fidelity source

Measurement independence can be significantly relaxed while still demonstrating nonlocality

Broader range of measurement dependent models excluded compared to CHSH inequality

Abstract

Quantum nonlocality stands as a resource for Device Independent Quantum Information Processing (DIQIP), as, for instance, Device Independent Quantum Key Distribution. We investigate experimentally the assumption of limited Measurement Dependence, i.e., that the measurement settings used in Bell inequality tests or DIQIP are partially influenced by the source of entangled particle and/or by an adversary. Using a recently derived Bell-like inequality [Phys. Rev. Lett. 113 190402] and a 99% fidelity source of partially entangled polarization photonic qubits, we obtain a clear violation of the inequality, excluding a much larger range of measurement dependent local models than would be possible with an adapted Clauser, Horne, Shimony and Holt (CHSH) inequality. It is therefore shown that the Measurement Independence assumption can be widely relaxed while still demonstrating quantum nonlocality.