Emergent Universality in a Quantum Tricritical Dicke Model

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.

Interplay of quantum phase transition and flat band in hybrid lattices

“…1(b)]. The superradiant QPT (a second-order phase transition) was proposed in the single Dicke model and occurs when increasing the atom-field coupling through a critical point [39][40][41][42][43][44][45][46][47][48][49][50][51], which is associated with a spontaneously Z 2 symmetry breaking. Extending to the periodic lattice, however, here we find that this critical point is replaced by the critical curves periodically modulated by wave number k. The periodical boundaries of normal and superradiant phases intersect at some certain values of k. This predicts, in the lattice systems, a critical region between the normal and superradiant phases, where the first-order phase transition and unstable phases alternatively appear in the different range of k.…”

Quantum tricritical point emerging in the spin-boson model with two dissipative spins in staggered biases

“…While in the latter model, it was demonstrated in Ref. [20] that the field can driven the 2nd QPTs in the Dicke model to the 1st-order, thus 2nd-order critical line can meet 1st-order critical line at the QuTP.…”

“…the qubit number N → ∞, exhibiting the mean-field critical behavior. The generalized Dicke models in the limit of N → ∞, such as the anisotropic Dicke model [17,18], the anisotropic Dicke model with the Stark coupling terms [19], and the Dicke model where infinite atoms are separated equally into two parts, each experiences an antiferromagnetic bias field [20] have been recently studied by several groups.…”

“…A quantum tricritical point (QuTP) [21] is seldomly supported in the solid-state materials, and is almost impossible to appear in the prototype models of the lightmatter interacting systems. Interestingly, it has been found to exist in anisotropic Dicke model [18] and the isotropic Dicke model with antiferromagnetic bias fields [20]. In the former model, the QuTP lies at the symmetric line of the superradiant "electric" and "magnetic" phases which can be mapped mutually by interchanging the rotating-wave term and the counterrotating one.…”

Finite-system Multicriticality at the Superradiant Quantum Phase Transition

“…At a multicritical point, the system is governed by a new universality class, which result in qualitatively different critical behaviors including new scaling fields and critical exponents [2]. Owing to this unique nature, intriguing features and novel universality classes have been found in various multicritical systems, including magnetic materials [3], superconductors [4], optical systems [5] and various condensed matter systems [6][7][8][9][10][11][12][13].…”