Quantum 2025 – scientific programme
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MON: Monday Contributed Sessions
MON 19: Foundational / Mathematical Aspects – Quantum Optics and Quantum Information
MON 19.6: Talk
Monday, September 8, 2025, 17:45–18:00, ZHG008
Outcome communication cannot explain nonlocality — Carlos Vieira1, •Carlos de Gois2,3, Sébastien Designolle4, Pedro Lauand5, Lucas E. A. Porto5,6, and Marco T. Quintino6 — 1IMECC, Unicamp, Brazil — 2Naturwissenschaftlich-Technische Fakultät, Uni Siegen, Germany — 3Inria, Université Paris-Saclay, France — 4Zuse Institute Berlin, Germany — 5IFGW, Unicamp, Brazil — 6LIP6, Paris, France
Sixty years ago it was established that quantum theory cannot be completed by local hidden variables. This fact implies a fundamental separation between classical and quantum systems, and has since become a central aspect of quantum information. However, it does not rule out the possibility of non-local completions. In particular, it is known that local hidden variable models augmented with two bits of classical communication can explain the correlations of any two-qubit state. Would this still hold if communication is restricted to measurement outcomes? We show that any qubit-qudit state can be explained by outcome communication if and only if it is local. In other words, outcome communication does not help explain qubit-qudit correlations. In contrast to the standard local model, where only rank-1 measurements must be reproduced, the outcome communication model must explicitly account for full-rank measurements. This is not a limitation of our proof, but a general fact. To prove this, we construct an explicit outcome-local model for all rank-1 measurements on a nonlocal state, thus showing that the equivalence between the two models does not hold for these measurements alone.
Keywords: correlations; nonlocality; communication