On the Quantum Chromatic Gap

Fuente: arXiv
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Autore principale: Ciardo, Lorenzo
Natura: Preprint
Pubblicazione: 2025
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author Ciardo, Lorenzo
author_facet Ciardo, Lorenzo
contents The largest known gap between quantum and classical chromatic number of graphs, obtained via quantum protocols for colouring Hadamard graphs based on the Deutsch--Jozsa algorithm and the quantum Fourier transform, is exponential. We put forth a quantum pseudo-telepathy version of Khot's $d$-to-$1$ Games Conjecture and prove that, conditional to its validity, the gap is unbounded: There exist graphs whose quantum chromatic number is $3$ and whose classical chromatic number is arbitrarily large. Furthermore, we show that the existence of a certain form of pseudo-telepathic XOR games would imply the conjecture and, thus, the unboundedness of the quantum chromatic gap. As two technical steps of our proof that might be of independent interest, we establish a quantum adjunction theorem for Pultr functors between categories of relational structures, and we prove that the Dinur--Khot--Kindler--Minzer--Safra reduction, recently used for proving the $2$-to-$2$ Games Theorem, is quantum complete.
format Preprint
id arxiv_https___arxiv_org_abs_2503_23207
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle On the Quantum Chromatic Gap
Ciardo, Lorenzo
Quantum Physics
Computational Complexity
Logic in Computer Science
Combinatorics
81P45, 05C15
The largest known gap between quantum and classical chromatic number of graphs, obtained via quantum protocols for colouring Hadamard graphs based on the Deutsch--Jozsa algorithm and the quantum Fourier transform, is exponential. We put forth a quantum pseudo-telepathy version of Khot's $d$-to-$1$ Games Conjecture and prove that, conditional to its validity, the gap is unbounded: There exist graphs whose quantum chromatic number is $3$ and whose classical chromatic number is arbitrarily large. Furthermore, we show that the existence of a certain form of pseudo-telepathic XOR games would imply the conjecture and, thus, the unboundedness of the quantum chromatic gap. As two technical steps of our proof that might be of independent interest, we establish a quantum adjunction theorem for Pultr functors between categories of relational structures, and we prove that the Dinur--Khot--Kindler--Minzer--Safra reduction, recently used for proving the $2$-to-$2$ Games Theorem, is quantum complete.
title On the Quantum Chromatic Gap
topic Quantum Physics
Computational Complexity
Logic in Computer Science
Combinatorics
81P45, 05C15
url https://arxiv.org/abs/2503.23207