Spontaneous polarized phase transitions and symmetry breaking in the imbalanced Dicke model

Abstract:We investigate the ground-state properties and quantum phase transitions of an ensemble consisting of $N$ four-level atoms within an optical cavity coupled to the single cavity mode and external laser fields. The system is described by an extended imbalanced Dicke model, in which the co- and counterrotating coupling terms are allowed to have different coupling strengths. Some novel polarized phases characterized by the phase differences between the cavity field or the atomic spin excitation and the Raman laser are found analytically. Meanwhile, the full phase diagram and quantum phase transitions are also revealed. Two sign-dependent coexisting phases have been identified, where the normal phase persists as a metastable state alongside the superradiant ground state. Finally, the breaking or restoration of the intrinsic symmetry in this system is addressed. It is found that besides the continuous $U(1)$ and discrete $\mathbb{Z}_2$ symmetries, the system also exhibits two reflection symmetries $\sigma_v$s, a central symmetry $C_2$ in the abstract position-momentum representation, and a discrete reflection parity-time ($\mathcal{PT}$) symmetry, a parameter exchange symmetry $\mathcal{T}_\mathrm{ex}$ in the parameter space. These additional symmetries are governed by two Coxeter groups.

arXiv:2408.10121 [quant-ph]

(or arXiv:2408.10121v2 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2408.10121 Focus to learn more arXiv-issued DOI via DataCite

https://doi.org/10.1088/1572-9494/aeacb4 Focus to learn more DOI(s) linking to related resources

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