Frustrated Superradiant Phase Transition

Frustration occurs when a system cannot satisfy competing interactions. In this talk, we introduce a frustrated superradiant phase transition [1] that occurs when the ground-state coherence of bosonic modes due to the strong local qubit-boson interaction cannot simultaneously minimize the positive hopping energies. As a model system, we consider the Dicke trimer model with negative and positive hopping energy and show that the latter leads to a sixfold degenerate ground-state manifold where the translational symmetry is spontaneously broken by frustration. Moreover, we find two sets of diverging time and fluctuation scales coexist in the frustrated superradiant phase. In addition to the mean-field critical mode present in the non-frustrated superradiant phase, a frustrated mode with a novel critical exponent emerges. The new critical exponent is associated with the fluctuation in the difference between local order parameters, which results in site-dependent photon number critical exponents. We provide the physical intuition behind the exotic critical scaling and generalize it to a Dicke lattice system with an odd number of sites. Our study paves the way to study frustrated phases of light-matter systems, as the frustration mechanism identified here can be applied to any lattice system where the antiferromagnetic ordering is incompatible with the lattice geometry.

[1] Jinchen Zhao and Myung-Joong Hwang, Phys. Rev. Lett. 128, 163601 (2022)