Floquet Engineering of a Quasiequilibrium Superradiant Phase Transition in Landau Polaritons

TL;DR

This paper demonstrates how Floquet engineering can induce superradiant phase transitions in a Landau polariton system, overcoming equilibrium no-go theorems by using off-resonant AC magnetic fields.

Contribution

It introduces a novel Floquet-based method to achieve superradiant phase transitions in a Landau polariton system, bypassing traditional constraints.

Findings

Floquet driving enables superradiant phase transition in a Landau polariton system.

Off-resonant AC magnetic field modulates system parameters to reach critical threshold.

The resulting phase exhibits photon condensation and Landau-level polarization.

Abstract

Superradiant phase transitions (SRPTs), characterized by photon condensation and macroscopic matter polarization, are forbidden in equilibrium for homogeneous fields by no-go theorems. Here, we show that Floquet driving can circumvent this constraint in a Landau polariton system consisting of a two-dimensional electron gas coupled to a terahertz cavity in a DC magnetic field. An off-resonant AC magnetic field modulates the cyclotron frequency and light--matter coupling strength while leaving the diamagnetic term unchanged, generating an additional DC coupling contribution. This drives the system across a critical threshold into a superradiant phase, characterized by photon condensation and Landau-level polarization in the ground state of the Floquet Hamiltonian. This quasiequilibrium approach offers a route to SRPTs distinct from driven-dissipative schemes.