Fig. 1: Passing gravitational waves result in stimulated absorption of gravitons.

Due to very low interaction strength, this can be used to design a gravito-phononic analog of the photoelectric effect with acoustic resonators to detect single gravitons. The resonator is cooled to the ground state and its first excited energy level is weakly monitored through continuous quantum sensing. A quantum jump from the ground state to the first excited state corresponds to a single-graviton detection event. Ideal system parameters for such events are given in Table 1. For GWs in the LIGO sensitivity window, correlating the signal to the classical LIGO detection provides confirmation of a single graviton absorption from an incident gravitational wave.