Apparatus and method establish quantum oscillations at room temperature. A cavity has therein a resonator structure that includes a resonant element and a gain medium. A species of the gain medium has an electronic spin multiplicity capable of supporting a two-level spin system. An optical pump pumps the resonator structure and thereby generates microwave output power through stimulated emission of thermal photons. The species of the gain medium is of a sufficiently high concentration such as to have an ensemble spin-photon coupling rate which exceeds both the cavity mode decay rate and the spin-spin decoherence rate. The optical pump pumps the resonator structure using a short pulse of nanosecond duration, or a burst of approximately a millisecond in duration at relatively low instantaneous optical power, to excite said species of the gain medium into a spin-polarized two-level system that exhibits quantum oscillations in the microwave output power.