Ultrahigh Q-frequency product for optomechanical disk resonators with a mechanical shield

We report on optomechanical GaAs disk resonators with ultrahigh quality factor-frequency product Q×f. Disks standing on a simple pedestal exhibit GHz mechanical breathing modes attaining a Q×f of 1013 measured under vacuum at cryogenic temperature. Clamping losses are found to be the dominant source of dissipation. An improved disk resonator geometry integrating a shield within the pedestal is then proposed, and its working principles and performances are investigated by numerical simulations. For dimensions compatible with fabrication constraints, the clamping-loss-limited Q reaches 107–109 corresponding to Q×f equals 1016–1018. This shielded pedestal approach applies to any heterostructure presenting an acoustic mismatch.