Superradiant quantum phase transition can be easier with disorder

We investigate the influence of strong static disorder on the transition frequency of molecules to the superradiant quantum phase transition in the Dicke model. A spin-fermion mapping is employed to recast the Dicke model into a coupled fermion-boson problem, which is subsequently treated by the non-equilibrium Green's function formalism. An analytical expression for the critical point as a function of the disorder strength is derived. In particular, there exists a regime where increasing the disorder strength reduces the critical coupling strength.