Limited measurement dependence in multiple runs of a Bell test

TL;DR

This paper investigates how limited measurement independence across multiple Bell test runs affects quantum violation thresholds, demonstrating that certain Bell violations remain secure against classical attacks even with some measurement dependence.

Contribution

It provides an analysis of measurement dependence correlations over multiple runs, establishing bounds where Bell violations are still secure against classical simulation.

Findings

Bell violations persist with high, non-maximal free will even when measurement choices are correlated across runs

Explicit optimal cheating strategies are characterized under measurement dependence

Security thresholds are identified for measurement dependence in multi-run Bell tests

Abstract

The assumption of free will - the ability of an experimentalist to make random choices - is central to proving the indeterminism of quantum resources, the primary tool in quantum cryptography. Relaxing the assumption in a Bell test allows violation of the usual classical threshold by correlating the random number generators used to select measurements with the devices that perform them. In this paper, we examine not only these correlations, but those across multiple runs of the experiment. This enables an explicit exposition of the optimal cheating strategy and how the correlations manifest themselves within this strategy. Similar to other recent results, we prove that there remain Bell violations for a sufficiently high, yet non-maximal degree of free will which cannot be simulated by a classical attack, regardless of how many runs of the experiment those choices are correlated over.