Fermi's golden rule does not adequately describe Dicke's superradiance

Abstract

We consider the application of Fermi's golden rule to the problem of N atoms, one of which is excited, in an extended medium with dimensions that are large compared with the wavelength. We find that, in contrast to an often-voiced opinion, the golden rule does not describe the physics of one photon absorbed and subsequently emitted by N atoms. The correct treatment includes many-body effects such as Fano interference. For a finite atomic cloud with size R, in the Markovian limit, the system will decay exponentially at a rate of around N(λ2/R 2) faster than the single-atom decay rate.