The effects of reduced "free will" on Bell-based randomness expansion

TL;DR

This paper investigates how reducing the assumption of free will in Bell tests impacts the security and effectiveness of quantum randomness expansion, providing bounds on adversarial capabilities under these conditions.

Contribution

It introduces a no-signalling model with diminished free will and derives bounds on an adversary's ability to compromise quantum randomness expansion.

Findings

Reduced free will weakens the security guarantees of Bell-based randomness expansion

Bounds on adversary capabilities are established under no-signalling assumptions

The study highlights the importance of free will in quantum cryptographic security

Abstract

With the advent of quantum information, the violation of a Bell inequality is used as evidence of the absence of an eavesdropper in cryptographic scenarios such as key distribution and randomness expansion. One of the key assumptions of Bell's Theorem is the existence of experimental "free will", meaning that measurement settings can be chosen at random and independently by each party. The relaxation of this assumption potentially shifts the balance of power towards an eavesdropper. We consider a no-signalling model with reduced "free will" and bound the adversary's capabilities in the task of randomness expansion.