Proposal for a Detector of Photons with Zero Projection of Spin

We suggest an indirect method of detection of photons with zero projection of spin mediated by emission of terahertz photons. This terahertz source is based on a system of microcavity exciton polaritons in the regime of polariton BEC formation when the cavity photons acquire an effective mass being localised in the cavity and therefore receive the third spin degree of freedom (corresponding to the longitudinal polarization with chirality l = 0). The optical transitions can occur between two polariton ground states based on the light-hole and heavy-hole excitons, respectively, accompanied by the emission of terahertz radiation with controllable characteristics. We calculate the dipole matrix element of such transitions and corresponding rate of spontaneous emission for a realistic cavity based on InAlGaAs alloys, investigate its dynamics and estimate quantum efficiency of the terahertz source.