Ultrastrong Coupling Experiments With Superradiant Meta-Atoms

In this contribution, we study the effects arising when using a metamaterial surface featuring a dense array of superradiant emitters as cavities for experiments in the ultrastrong coupling regime. We show that an increasing cavity loss does not always lead to the expected transition to the weakly coupled Purcell regime but more that it is still possible to observe polaritons as a feature of the strong, coupling between the meta atoms and the intersubband transition.