Dresden 2026 – scientific programme

Parts | Days | Selection | Search | Updates | Downloads | Help

QI: Fachverband Quanteninformation

QI 12: Quantum Foundations

QI 12.3: Talk

Wednesday, March 11, 2026, 15:30–15:45, BEY/0137

Paradox-free classical non-causality and unambiguous nonlocality without entanglement are equivalent — Hippolyte Dourdent¹, Kyrylo Simonov², •Andreas Leitherer¹, Emanuel-Cristian Boghiu², Ravi Kunjwal³, Saronath Halder⁴, Remigiusz Augusiak⁴, and Antonio Acín^{1, 5} — ¹ICFO-Institut de Ciències Fotòniques — ²Fakultät für Mathematik, Universität Wien — ³Aix-Marseille University, CNRS, LIS — ⁴Center for Theoretical Physics, Polish Academy of Sciences — ⁵ICREA - Institució Catalana de Recerca i Estudis Avançats

Definite causal order is an intuitive assumption which can, however, be violated without introducing paradoxes such as the grandfather antinomy. Interestingly, it is not necessary to invoke quantum or more exotic physics: process functions generalize classical deterministic communication by relaxing the assumption of a fixed causal structure between local operations. Previous work demonstrated that for three-parties, non-causal process functions can distinguish qubit product bases that cannot be realized by local operations and classical communication - a phenomenon known as quantum nonlocality without entanglement (QNLWE). We significantly elevate this result for any dimension and any number of parties, establishing an equivalence between the unique fixed-point condition characterizing process functions and a simple ``unambiguity" condition, requiring that local parties perform local disjoint operations. We refine previous characterizations of process functions and demonstrate how to construct non-causal process functions from unambiguous QNLWE product bases and vice versa.

Keywords: Causality; Indefinite causal order; Quantum nonlocality without entanglement