  It is shown that currents in thin-film superconducting rings irradiated by
coherent microwave fields, can discretely decay with photons emission. These
quantized jumps of the supercurrent correspond to destruction one or several
magnetic flux quanta trapped in the ring. The ring thickness should be less
than the skin-depth of the low-frequency field. The probability of the
microwave field-induced single-photon decay of the supercurrent states in these
rings is obtained. The angle distributions of the photons emitted by
superconducting rings, and the current state lifetimes, depending on the ring
sizes and the fluxoid numbers in the initial states, are studied.
