Influence of counter-rotating interaction on quantum phase transition in Dicke-Hubbard lattice: an extended coherent state approach

TL;DR

This paper studies how counter-rotating interactions affect quantum phase transitions in the Dicke-Hubbard lattice using an extended coherent state approach, revealing new localization-delocalization behavior and phase boundary stabilization.

Contribution

It introduces a generalized extended coherent state method within mean-field theory to analyze the Dicke-Hubbard model with counter-rotating terms, highlighting novel phase transition characteristics.

Findings

Quantum phase transition involves parity symmetry breaking.

Mott lobes are suppressed with increasing coupling.

Phase boundaries are stabilized by decreasing photon hopping.

Abstract

We investigate the ground state behavior of the Dicke-Hubbard model including counter-rotating-terms. By generalizing an extended coherent state approach within mean-field theory, we self-consistently obtain the ground state energy and delocalized order parameter. Localization-delocalization quantum phase transition of photons is clearly observed by breaking the parity symmetry. Particularly, Mott lobes are fully suppressed, and the delocalized order parameter shows monotonic enhancement by increasing qubit-cavity coupling strength, in sharp contrast to the Dicke-Hubbard model under rotating-wave approximation. Moreover, the corresponding phase boundaries are stabilized by decreasing photon hopping strength, compared to the Rabi-Hubbard model.