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  • Letter
  • Open Access

Krylov complexity in mixed phase space

Kyoung-Bum Huh1, Hyun-Sik Jeong2, Leopoldo A. Pando Zayas3,4, and Juan F. Pedraza2

Phys. Rev. D 111, L121902 – Published 16 June, 2025

DOI: https://doi.org/10.1103/gmy7-dn7l

Abstract

We investigate the Krylov complexity of thermofield double states in systems with mixed phase space, uncovering a direct correlation with the Brody distribution, which interpolates between Poisson and Wigner statistics. Our analysis spans two-dimensional random matrix models featuring (I) GOE-Poisson and (II) GUE-Poisson transitions and extends to higher-dimensional cases, including a stringy matrix model (GOE-Poisson) and the mass-deformed SYK model (GUE-Poisson). Krylov complexity consistently emerges as a reliable marker of quantum chaos, displaying a characteristic peak in the chaotic regime that gradually diminishes as the Brody parameter approaches zero, signaling a shift toward integrability. These results establish Krylov complexity as a powerful diagnostic of quantum chaos and highlight its interplay with eigenvalue statistics in mixed phase systems.

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