Ultrasensitive and high resolution mass sensor by photonic-molecule optomechanics with phonon pump

Abstract

Whispering gallery mode cavities, due to their high quality factors, small mode volumes, and simple fabrications, have potential applications in photonic devices and ultrasensitive mass sensing. Cavity optomechanic systems based on whispering gallery mode cavities have draw tremendous attention in recent years due to the fact that they reveal and explore fundamental quantum physics and pave the way for potential applications of optomechanical devices. Unfortunately, whispering gallery mode based cavity optomechanics still lies in a single optical mode coupled to a single mechanical mode. Here, in this work, we propose an ultrasensitive and high resolution optical mass sensor by photonic-molecule optomechanics driven by two-tone field, where the optomechanical cavity driven by a weak coherent phonon pump is coupled to an auxiliary optical cavity. The auxiliary cavity plays the role of decreasing the mechanical damping rate while the weak coherent phonon pump to the mechanical mode will improve the intensity of the probe transmission spectrum, which together enhance the mass sensitivity. Compared with the optical mass sensor based on single-cavity optomechanics, the mass sensitivity presented here is improved significantly. We also investigate different parameter regimes which guide us to choose the optimal parameters. Finally, we illustrate the accurate measurement for the mass of nanoparticles, and the photonic-molecule optomechanics system will provide a new platform for exploring the on-chip applications in ultrahigh resolution sensing devices.