Entropy and singular-value moments of products of truncated random unitary matrices

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1. Verfasser: Beenakker, C. W. J.
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Veröffentlicht: 2025
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author Beenakker, C. W. J.
author_facet Beenakker, C. W. J.
contents Products of truncated unitary matrices, independently and uniformly drawn from the unitary group, can be used to study universal aspects of monitored quantum circuits. The von Neumann entropy of the corresponding density matrix decreases with increasing length $L$ of the product chain, in a way that depends on the matrix dimension $N$ and the truncation depth $δN$. Here we study that dependence in the double-scaling limit $L,N\rightarrow\infty$, at fixed ratio $τ=LδN/N$. The entropy reduction crosses over from a linear to a logarithmic dependence on $τ$ when this parameter crosses unity. The central technical result is an expression for the singular-value moments of the matrix product in terms of the Erlang function from queueing theory.
format Preprint
id arxiv_https___arxiv_org_abs_2501_11085
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Entropy and singular-value moments of products of truncated random unitary matrices
Beenakker, C. W. J.
Quantum Physics
Statistical Mechanics
Mathematical Physics
Products of truncated unitary matrices, independently and uniformly drawn from the unitary group, can be used to study universal aspects of monitored quantum circuits. The von Neumann entropy of the corresponding density matrix decreases with increasing length $L$ of the product chain, in a way that depends on the matrix dimension $N$ and the truncation depth $δN$. Here we study that dependence in the double-scaling limit $L,N\rightarrow\infty$, at fixed ratio $τ=LδN/N$. The entropy reduction crosses over from a linear to a logarithmic dependence on $τ$ when this parameter crosses unity. The central technical result is an expression for the singular-value moments of the matrix product in terms of the Erlang function from queueing theory.
title Entropy and singular-value moments of products of truncated random unitary matrices
topic Quantum Physics
Statistical Mechanics
Mathematical Physics
url https://arxiv.org/abs/2501.11085