Time-dependent photon generation by superconducting thin-film rings irradiated by coherent microwave fields

When a thin-film ring with supercurrent is irradiated by coherent microwave field, the field induces coherent oscillations of all the Cooper pairs involved in the supercurrent. The oscillating charged condensate will emit photons with energies determined by the difference of quantized energy levels of the superconducting ring. This effect can be observed only in the rings, the thickness of which is less than both the field skin-depth and the London penetration depth. The probability of the microwave field-induced single-photon and two-photon emission is calculated. The energy - angle distributions of the emitted photons as a function of both the ring sizes and the fluxoid number trapped in the ring, are explored.