Hierarchic superradiant phases in anisotropic Dicke model

TL;DR

This paper explores the complex phase structure of an anisotropic Dicke model, identifying hierarchic superradiant phases through dynamical analysis and numerical simulations, revealing new effective Hamiltonian regimes.

Contribution

It uncovers hierarchic superradiant phases in the anisotropic Dicke model by analyzing non-analyticities and exceptional points, introducing a dynamical characterization via Loschmidt echo.

Findings

Identification of three distinct superradiant regimes with different effective Hamiltonians

Demonstration of non-analyticities linked to exceptional points in the phase diagram

Numerical confirmation of hierarchic superradiant phases in finite systems

Abstract

We revisit the phase diagram of an anisotropic Dicke model by revealing the non-analyticity induced by underlying exceptional points. We find that, from a dynamical perspective, the conventional superradiant phase can be further separated into three regions, in which the systems are characterized by different effective Hamiltonians, including the harmonic oscillator, the inverted harmonic oscillator, and their respective counterparts. We employ the Loschmidt echo to characterize different quantum phases by analyzing the quench dynamics of a trivial initial state. Numerical simulations for finite systems confirm our predictions about the existence of hierarchic superradiant phases.