Solvable relaxation in discrete unitary systems: Ruelle-Pollicott resonances and CMV matrices
Abstract
Leading eigenvalues of the truncated propagator, known as Ruelle-Pollicott (RP) resonances, are an elegant way of addressing the dynamics of unitary many-body systems. We study unitary propagators in their canonical form, known in the mathematical literature as the CMV matrices, and obtain a number of exact results for RP resonances and the associated norm-diverging eigenvectors. For the simplest CMV class describing a unilateral shift with an impurity, motivated by operator dynamics in dual-unitary circuits, we obtain closed-form results and in particular show that the three independent ways of obtaining RP resonances -- the truncated propagator, analytic continuation of the resolvent, and the rigged Hilbert space approach -- all give the same results. In more realistic CMV matrices, in which shift-like operator dynamics characteristic of chaotic systems is only asymptotic, we rely on the rich theory of orthogonal polynomials on the unit circle and identify two phases. In the first phase, relaxation occurs due to local operators effectively evolving into increasingly nonlocal ones with negligible backflow. Especially interesting is the second phase, which, surprisingly, exhibits faster relaxation because of contributions from the backflow of large operators. Additionally, in the second phase, RP resonances are not equal to the eigenvalues of the truncated propagator, instead, they are ``hidden'' within a ring of ill-conditioned eigenvalues.
Related
- On Solving Continuous-Discrete Projection Filters via Sum-of-Squares Relaxation
- Fully discrete energy stability for a one-dimensional hyperbolic relaxation model with complete topography terms
- Extending Pathwise Gradients to Discrete Random Variables via Finite-Order Relaxation
- Dirichlet--Neumann waveform relaxation for heterogeneous heat equations: fully discrete l2 analysis
- Dirichlet-Neumann waveform relaxation for heterogeneous heat equations: continuous and time discrete L2 analysis
BibTeX
@misc{duh2026solvable,
title = {{Solvable relaxation in discrete unitary systems: Ruelle-Pollicott resonances and CMV matrices}},
author = {Urban Duh and Friedrich Hübner and Marko Žnidarič},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2608.28575},
eprint = {2608.28575},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.28575},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Solvable relaxation in discrete unitary systems: Ruelle-Pollicott resonances and CMV matrices
AU - Urban Duh
AU - Friedrich Hübner
AU - Marko Žnidarič
PY - 2026
DA - 2026/09/11
PB - arXiv
DO - 10.48550/arxiv.2608.28575
UR - https://arxiv.org/abs/2608.28575
AB - Leading eigenvalues of the truncated propagator, known as Ruelle-Pollicott (RP) resonances, are an elegant way of addressing the dynamics of unitary many-body systems. We study unitary propagators in their canonical form, known in the mathematical literature as the CMV matrices, and obtain a number of exact results for RP resonances and the associated norm-diverging eigenvectors. For the simplest CMV class describing a unilateral shift with an impurity, motivated by operator dynamics in dual-unitary circuits, we obtain closed-form results and in particular show that the three independent ways of obtaining RP resonances -- the truncated propagator, analytic continuation of the resolvent, and the rigged Hilbert space approach -- all give the same results. In more realistic CMV matrices, in which shift-like operator dynamics characteristic of chaotic systems is only asymptotic, we rely on the rich theory of orthogonal polynomials on the unit circle and identify two phases. In the first phase, relaxation occurs due to local operators effectively evolving into increasingly nonlocal ones with negligible backflow. Especially interesting is the second phase, which, surprisingly, exhibits faster relaxation because of contributions from the backflow of large operators. Additionally, in the second phase, RP resonances are not equal to the eigenvalues of the truncated propagator, instead, they are ``hidden'' within a ring of ill-conditioned eigenvalues.
ER -