Closing the problem of which causal structures of up to six total nodes have a classical-quantum gap

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Hauptverfasser: Khanna, Shashaank, Pusey, Matthew, Colbeck, Roger
Format: Preprint
Veröffentlicht: 2025
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author Khanna, Shashaank
Pusey, Matthew
Colbeck, Roger
author_facet Khanna, Shashaank
Pusey, Matthew
Colbeck, Roger
contents The discovery of Bell that there exist quantum correlations that cannot be reproduced classically is one of the most important in the foundations of quantum mechanics, as well as having practical implications. Bell's result was originally proven in a simple bipartite causal structure, but analogous results have also been shown in further causal structures. Here we study the only causal structure with six or fewer nodes in which the question of whether or not there exist quantum correlations that cannot be achieved classically was open. In this causal structure we show that such quantum correlations exist using a method that involves imposing additional restrictions on the correlations. This hence completes the picture of which causal structures of up to six nodes support non-classical quantum correlations. We also provide further illustrations of our method using other causal structures.
format Preprint
id arxiv_https___arxiv_org_abs_2512_04058
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Closing the problem of which causal structures of up to six total nodes have a classical-quantum gap
Khanna, Shashaank
Pusey, Matthew
Colbeck, Roger
Quantum Physics
Machine Learning
Statistics Theory
The discovery of Bell that there exist quantum correlations that cannot be reproduced classically is one of the most important in the foundations of quantum mechanics, as well as having practical implications. Bell's result was originally proven in a simple bipartite causal structure, but analogous results have also been shown in further causal structures. Here we study the only causal structure with six or fewer nodes in which the question of whether or not there exist quantum correlations that cannot be achieved classically was open. In this causal structure we show that such quantum correlations exist using a method that involves imposing additional restrictions on the correlations. This hence completes the picture of which causal structures of up to six nodes support non-classical quantum correlations. We also provide further illustrations of our method using other causal structures.
title Closing the problem of which causal structures of up to six total nodes have a classical-quantum gap
topic Quantum Physics
Machine Learning
Statistics Theory
url https://arxiv.org/abs/2512.04058