Terahertz photon production from cold atoms inside an optical cavity

Abstract

The Dicke model was proposed by Dicke in 1954 to describe a single mode of photon coupled to an assembly of N atoms with the same strength. It was found that there is a quantum phase transition from a normal phase at weak coupling to a super-radiant phase at strong coupling at the thermodynamic limit N =∞. Here, we solve the model at N ≥ 1 and also discuss its possible experimental implementations inside a cavity. By studying the Dicke model by 1/N expansion, we identify an emergent quantum phase diffusion mode inside the super-radiant phase and also work out many remarkable experimental consequences of this mode such as its low frequency, photon number squeezing properties and photon statistics. The energy of the phase diffusion modecan be continuously tuned into many frequency ranges from Micro-wave to Terahertz (THz) to Infra-red. The photons from the super-radiant phase are in a number squeezed state with much enhanced signal/noise ratio which may have wide applications in quantum information processing. The photon statistics is strong sub-Poissonian. The effects of dissipations due to leaking photons out of the cavity are also discussed. The connections with the recent experiments of the strong coupling of a BEC of N ~ 10 5 87 Rb atoms to the photons inside an ultrahigh-finess optical cavity are carefully analyzed. Several experimental schemes to detect the phase diffusion mode are proposed.