# Emergent Universality in a Quantum Tricritical Dicke Model

## TL;DR

This paper introduces a generalized Dicke model with a quantum tricritical point, revealing universal relations between excitation gap and entanglement entropy along the critical line, despite non-universality of the order parameter.

## Contribution

It presents a novel quantum tricritical Dicke model and uncovers universal quantum behavior linked to emergent modes at criticality.

## Key findings

- Universal relation between excitation gap and entanglement entropy
- Non-universality of the order parameter at the tricritical point
- Separation of classical and quantum degrees of freedom

## Abstract

We propose a generalized Dicke model which supports a quantum tricritical point. We map out the phase diagram and investigate the critical behaviors of the model through exact low-energy effective Hamiltonian in the thermodynamic limit. As predicted by the Landau theory of phase transition, the order parameter shows non-universality at the tricritical point. Nevertheless, as a result of the separation of the classical and the quantum degrees of freedom, we find a universal relation between the excitation gap and the entanglement entropy for the entire critical line including the tricritical point. Here the universality is carried by the emergent quantum modes, whereas the order parameter is determined classically.