Quantum chaos for nonstandard symmetry classes in the Feingold-Peres model of coupled tops

TL;DR

This paper explores the quantum chaos properties of a coupled tops model, revealing nonstandard symmetries beyond traditional classes, and demonstrates that spectral signatures align with random-matrix theory predictions in chaotic regimes.

Contribution

It identifies nonstandard symmetry classes in the Feinberg-Peres model and analyzes their spectral signatures, extending the understanding of quantum chaos beyond standard symmetry classifications.

Findings

Spectral signatures match Gaussian ensembles in chaotic regimes.

Nonstandard symmetries are identified in the coupled tops model.

Signatures diminish or change in mixed or near-integrable dynamics.

Abstract

We consider two coupled quantum tops with angular momentum vectors $\mathbf{L}$ and $\mathbf{M}$. The coupling Hamiltonian defines the Feinberg-Peres model which is a known paradigm of quantum chaos. We show that this model has a nonstandard symmetry with respect to the Altland-Zirnbauer tenfold symmetry classification of quantum systems which extends the well-known threefold way of Wigner and Dyson (referred to as `standard' symmetry classes here). We identify that the nonstandard symmetry classes BD$I_0$ (chiral orthogonal class with no zero modes), BD$I_1$ (chiral orthogonal class with one zero mode) and C$I$ (antichiral orthogonal class) as well as the standard symmetry class A$I$ (orthogonal class). We numerically analyze the specific spectral quantum signatures of chaos related to the nonstandard symmetries. In the microscopic density of states and in the distribution of the lowest positive energy eigenvalue we show that the Feinberg-Peres model follows the predictions of the Gaussian ensembles of random-matrix theory in the appropriate symmetry class if the corresponding classical dynamics is chaotic. In a crossover to mixed and near-integrable classical dynamics we show that these signatures disappear or strongly change.