Superradiant to subradiant phase transition in the open system Dicke model: Dark state cascades

Collectivity in ensembles of atoms gives rise to effects like superand subradiance. While superradiance is well studied and experimentally accessible, subradiance remains elusive since it is difficult to track experimentally as well as theoretically. Here we present a new type of phase transition in the resonantly driven, open Dicke model that leads to a deterministic generation of subradiant states. At the transition the system switches from a predominantly superradiant to a predominantly subradiant state. Clear experimental signatures for the effect are presented and entanglement properties are discussed. Letting the system relax into the ground state generates a cascade of dark Dicke states, with dark state populations up to unity. Furthermore we introduce a collectivity measure that allows to quantify collective behavior. 1 ar X iv :1 70 5. 02 88 9v 2 [ qu an tph ] 1 2 Ju l 2 01 7