Robust continuous symmetry breaking and multiversality in the chiral Dicke model

TL;DR

The paper introduces the chiral Dicke model, a generalized light-matter interaction system with continuous symmetry, revealing novel quantum phases and multiversal critical phenomena.

Contribution

It presents the chiral Dicke model with a continuous $U(1)$ symmetry and uncovers multiversality in its quantum phase transitions.

Findings

Identification of a $U(1)$-broken superradiant phase.

Demonstration of highly tunable quantum fluctuation spectra.

Discovery of multiversality with different critical exponents along a special parameter line.

Abstract

The Dicke model (DM) serves as a paradigm for understanding collective light-matter interactions. We introduce the chiral Dicke model, a generalization where an atomic ensemble couples to a two-mode cavity via chiral interactions. Unlike the standard DM, the chiral DM is endowed with an inherent continuous $U(1)$ symmetry associated with angular momentum conservation. The ground-state phase diagram and the associated quantum phase transitions are charted out, revealing a $U(1)$-broken superradiant phase that spans a broad parameter space. We demonstrate that the spectrum of quantum fluctuations is highly tunable in both the symmetric and broken phases. Strikingly, our calculations reveal that the system exhibits `multiversality', where distinct universality classes govern the transition between the same two phases. In particular, along a special line in parameter space, the dynamical critical exponent for the normal-superradiant phase transition changes from $z\nu=1$ to $z\nu=1/2$. Our work establishes the chiral Dicke model as a powerful platform to realize novel quantum phases and multiversal critical phenomena in light-matter coupled systems.