Quantum Criticality in the Biased Dicke Model

TL;DR

This paper investigates the biased Dicke model's critical behavior, revealing that finite bias prevents a second order phase transition and significantly alters ground state properties like squeezing and entanglement.

Contribution

It provides analytical insights into how bias affects phase transitions and ground state properties in the Dicke model, a topic not thoroughly explored before.

Findings

Excitation energy remains finite for all couplings in the biased model.

Second order phase transition is avoided due to bias.

Bias significantly modifies squeezing and entanglement near criticality.

Abstract

The biased Dicke model describes a system of biased two-level atoms coupled to a bosonic field, and is expected to produce new phenomena that are not present in the original Dicke model. In this paper, we study the critical properties of the biased Dicke model in the classical oscillator limits. For the finite-biased case in this limit, We present analytical results demonstrating that the excitation energy does not vanish for arbitrary coupling. This indicates that the second order phase transition is avoided in the biased Dicke model, which contrasts to the original Dicke model. We also analyze the squeezing and the entanglement in the ground state, and find that a finite bias will strongly modify their behaviors in the vicinity of the critical coupling point.