Optimized experimental settings for the best detection of quantum nonlocality

TL;DR

This paper derives explicit optimal experimental parameters for detecting quantum nonlocality across various states, revealing that these settings can change abruptly, even during system evolution, impacting the success of Bell tests.

Contribution

It provides explicit formulas for optimal measurement settings for a broad class of quantum states and highlights the possibility of discontinuous changes during state evolution.

Findings

Optimal parameters depend explicitly on the quantum state.

Suitable settings may change abruptly with continuous state variation.

Discontinuous jumps in settings can occur during system evolution.

Abstract

Nonlocality lies at the core of quantum mechanics from both a fundamental and applicative point of view. It is typically revealed by a Bell test, that is by violation of a Bell inequality, whose success depends both on the state of the system and on parameters linked to experimental settings. This leads to find, given the state, optimized parameters for a successful test. Here we provide, for a quite general class of quantum states, the explicit expressions of these optimized parameters and point out that, for a continuous change of the state, the corresponding suitable experimental settings may unexpectedly vary discontinuously. We finally show in a paradigmatic open quantum system that this abrupt "jump" of the experimental settings may even occur during the time evolution of the system. These jumps must be taken into account in order not to compromise the correct detection of nonlocality in the system.