Electromagnetic-field-induced decay of currents in superconducting thin-film rings with photon emission

It is shown that superconducting currents in thin-film rings irradiated by coherent microwave field can decay with emission of photons. When the ring thickness is less than the field penetration depth, the field induces coherent oscillations of all the Cooper pairs in the ring. The oscillating condensate will emit photons with energies determined by the difference of quantized energy levels of the superconducting ring. The probability of the microwave field-induced single-photon decay of the supercurrents is calculated. The angular distributions of the photons emitted by the superconducting rings and the lifetimes of the current states, depending on both the ring sizes and the fluxoid numbers in the initial states, are studied.