From quantum Rabi model to Jaynes-Cummings model: symmetry-breaking quantum phase transitions, topological phase transitions and multicriticalities

TL;DR

This paper explores the complex phase transitions in the anisotropic quantum Rabi model, revealing hidden symmetry breaking, topological transitions, and multicritical points that connect it to the Jaynes-Cummings model.

Contribution

It uncovers the detailed phase diagram of the anisotropic QRM, identifying novel topological and multicritical phenomena that extend understanding of quantum phase transitions.

Findings

Second-order QPT in low frequency limit

Hidden symmetry breaking in phase transition

Series of topological and multicritical points

Abstract

We study the ground state (GS) and excitation gap of anisotropic quantum Rabi model (QRM) which connects the fundamental QRM and the Jaynes-Cummings model (JCM). While the GS has a second-order quantum phase transition (QPT) in the low frequency limit, turning on finite frequencies we shed a novel light on the phase diagram to illuminate a fine structure of first-order transition series. We find the QPT is accompanied with a hidden symmetry breaking, whereas the emerging series transitions are topological transitions without symmetry breaking. The topological structure of the wave function provides a novel universality classification in bridging the QRM and the JCM. We show that the conventionally established triple point is actually a quintuple or sextuple point and following the penta-/hexa-criticality emerge a series of tetra-criticalities.