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arXiv · 2408.03665

When Quantum Nonlocality Does Not Play Dice

Ravishankar Ramanathan·Yuan Liu·Stefano Pironio
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Abstract

Bell nonlocality is widely viewed as a signature of intrinsic randomness, effectively playing the role of a 'dice' at the heart of many device-independent cryptographic protocols. We show that this connection has a fundamental limitation: there exist Bell inequalities that are maximally violated by quantum correlations yet certify no randomness for any fixed input pair. We develop a systematic construction based on symmetric deterministic extensions of nonlocal games, and use it to obtain explicit examples of such inequalities. We also construct maximally nonlocal quantum correlations that, for every input pair, admit a convex decomposition into strategies with predetermined outputs for those inputs. Our results reveal a strong form of determinism compatible with quantum nonlocality and delineate the limits of device-independent randomness certification.

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Ravishankar Ramanathan, Yuan Liu, Stefano Pironio. 2024-08-07. When Quantum Nonlocality Does Not Play Dice. https://arxiv.org/abs/2408.03665

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