Symmetry breaking patterns, tricriticalities and quadruple points in quantum Rabi model with bias and nonlinear interaction

TL;DR

This paper explores complex symmetry breaking, tricritical points, and quadruple points in the quantum Rabi model with bias and nonlinear interactions, revealing novel quantum transitions beyond semiclassical predictions.

Contribution

It uncovers new quantum phase transitions, tricriticalities, and quadruple points caused by bias and nonlinear interactions in the quantum Rabi model, with analytical phase boundary insights.

Findings

Discovery of novel transitions and tricritical points.

Identification of quadruple points in the phase diagram.

Quantum effects significantly alter classical predictions.

Abstract

Quantum Rabi model (QRM) is fascinating not only because of its broad relevance and but also due to its few-body quantum phase transition. In practice both the bias and the nonlinear coupling in QRM are important controlling parameters in experimental setups. We study the interplay of the bias and the nonlinear interaction with the linear coupling in the ground state which exhibits various patterns of symmetry breaking and different orders of transitions. Several situations of tricriticality are unveiled in the low frequency limit and at finite frequencies. We find that the full quantum-mechanical effect leads to novel transitions, tricriticalities and quadruple points, which are much beyond the semiclassical picture. We clarify the underlying mechanisms by analyzing the energy competitions and the essential changeovers of the quantum states, which enables us to extract most analytic phase boundaries.