Classical chaos in atom-field systems

TL;DR

This paper investigates the relationship between chaos and quantum phase transitions in atom-field systems, using numerical analysis of the Dicke model to map chaos across different energies and couplings.

Contribution

It provides a detailed numerical study distinguishing the mechanisms of chaos and ESQPT in resonant and off-resonant atom-field systems.

Findings

Chaos onset varies with energy and coupling.

ESQPT and chaos are driven by different mechanisms.

Maps of ergodic regions in parameter space are presented.

Abstract

The relation between the onset of chaos and critical phenomena, like Quantum Phase Transitions (QPT) and Excited-State Quantum Phase transitions (ESQPT), is analyzed for atom-field systems. While it has been speculated that the onset of hard chaos is associated with ESQPT based in the resonant case, the off-resonant cases show clearly that both phenomena, ESQPT and chaos, respond to different mechanisms. The results are supported in a detailed numerical study of the dynamics of the semiclassical Hamiltonian of the Dicke model. The appearance of chaos is quantified calculating the largest Lyapunov exponent for a wide sample of initial conditions in the whole available phase space for a given energy. The percentage of the available phase space with chaotic trajectories is evaluated as a function of energy and coupling between the qubit and bosonic part, allowing to obtain maps in the space of coupling and energy, where ergodic properties are observed in the model. Different sets of Hamiltonian parameters are considered, including resonant and off-resonant cases.