Femtogram scale nanomechanical resonators embedded in a double-slot photonic crystal nanobeam cavity

Abstract

An optomechanical device that contains a nanomechanical resonator with an ultralow effective mass of 6.42 fg is designed and demonstrated. The femtogram scale nanomechanical resonator is embedded in a double-slot photonic crystal nanobeam cavity. Optical resonance provides efficient readout of the nanomechanical resonator movements. The fabricated device is optically and mechanically characterized in atmosphere. In the measured radio-frequency power spectral density, a peak at 3.928 GHz is identified to be the mechanical mode with an effective mass of 6.42 fg. The measured room-temperature mechanical Q-factor is 1255, and a displacement sensitivity of 0.13 fm/Hz, which is 22 times beyond the standard quantum limit, is obtained. These demonstrated on-chip integrated optomechanical devices combining high Q-factor optical cavities and nanomechanical resonators with ultralow effective masses are promising in ultrasensitive measurements.