Freeness Reined in by a Single Qubit

Fuente: arXiv
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Auteurs principaux: Altland, Alexander, Divi, Francisco, Micklitz, Tobias, Rezaei, Maedeh
Format: Preprint
Publié: 2025
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author Altland, Alexander
Divi, Francisco
Micklitz, Tobias
Rezaei, Maedeh
author_facet Altland, Alexander
Divi, Francisco
Micklitz, Tobias
Rezaei, Maedeh
contents Free probability provides a framework for describing correlations between non-commuting observables in complex quantum systems whose Hilbert-space states follow maximum-entropy distributions. We examine the robustness of this framework under a minimal deviation from freeness: the coupling of a single ancilla qubit to a Haar-distributed quantum circuit of dimension $D0 \gg 1$. We find that, even in this setting, the correlation functions predicted by free probability theory receive corrections of order $O(1)$. These modifications persist at long times, when the dynamics of the coupled system is already ergodic. We trace their origin to non-uniformly distributed stationary quantum states, which we characterize analytically and confirm numerically.
format Preprint
id arxiv_https___arxiv_org_abs_2512_13803
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Freeness Reined in by a Single Qubit
Altland, Alexander
Divi, Francisco
Micklitz, Tobias
Rezaei, Maedeh
Quantum Physics
Disordered Systems and Neural Networks
Free probability provides a framework for describing correlations between non-commuting observables in complex quantum systems whose Hilbert-space states follow maximum-entropy distributions. We examine the robustness of this framework under a minimal deviation from freeness: the coupling of a single ancilla qubit to a Haar-distributed quantum circuit of dimension $D0 \gg 1$. We find that, even in this setting, the correlation functions predicted by free probability theory receive corrections of order $O(1)$. These modifications persist at long times, when the dynamics of the coupled system is already ergodic. We trace their origin to non-uniformly distributed stationary quantum states, which we characterize analytically and confirm numerically.
title Freeness Reined in by a Single Qubit
topic Quantum Physics
Disordered Systems and Neural Networks
url https://arxiv.org/abs/2512.13803