Quantum magnetism meets cavity QED*

Light-matter interactions are fundamental for both studying and

controlling quantum materials. It is of particular interest to consider

the case of nonclassical light, which can increase the precision of

measurements as well as lead to new phenomena. A particular example is

the quantum battery which couples multiple charge units coherently to a

cavity. With the cavity-enhanced light-matter interactions, the

electrons form polariton states with coherent photons.

A paradigmatic model for light-matter interaction is the Dicke model,

which exhibits a transition between the normal and superradiant phases.

A natural progression is to combine the Dicke model with interacting

spin models. We investigate a family of spin models with increasing

complexity from Ising to compass models. Leveraging the recently

developed variational non-Gaussian ED (NGSED) method, we unveil the

effects of spin interactions within the normal-superradiant phase

diagram. Moreover, we reverse the lens, discerning the influence of

quantum light on the phase diagram of the spin system.