Loschmidt Echo and Classicality of the Gamma Model

TL;DR

This paper investigates the classicality of the Gamma Model using Loschmidt Echo and roughness measures, revealing integrability, stationary regimes, and the influence of Hilbert space size on classicality indicators.

Contribution

It provides a detailed analysis of the Gamma Model's classicality through overlap dynamics and roughness, highlighting stationary regimes and the role of Hilbert space size.

Findings

Overlap mean decays inversely with effective Hilbert space in non-periodic case

Two stationary regimes identified for overlap mean and variance

Roughness mean also exhibits two stationary regimes and depends on Hilbert space size

Abstract

The classicality of the Gamma Model, an analytically solvable quantum oscillator with non-linear dynamics, is investigated using the overlap dynamics, also known as the Loschmidt Echo, and roughness, a classicality measure based on the Wigner representation of a state. Though the overlap dynamics would indicate a chaotic regime, here the model is integrable. The time mean of the overlap function decays inversely with the effective Hilbert space occupied by the initial state for the non-periodic case. Two different stationary regimes were found for the overlap mean and overlap variance. The state non-classicality was investigated using the roughness measure, and its mean also has two stationary regimes. For large effective Hilbert space, the roughness time mean depends more on the effective space than the initial state. While the Wigner function is dominated by the non-diagonal terms, the overlap operator has some contribution on each part, but it is more affected by the diagonal terms than the density matrix.