Level Attraction due to Dissipative Phonon-Phonon Coupling in an Opto-Mechano-Fluidic Resonator

Dissipative couplings between solid-cavity optomechanical oscillators provide an underlying mechanism for many physical phenomena, such as level attraction, non-Hermitian parity-time symmetric, and topological energy transfer with exceptional points (EPs). Until now, cavity optomechanical mode couplings on different phases of material have not been demonstrated. Here, we report the experimental demonstration of optomechanical mode dissipative coupling, mediated by high-quality-factor photon whispering-gallery modes, between a solid surface wave mode (SWM) and a liquid radial breathing mode (RBM), both of which coexist in an optofluidic microbubble resonator consisting of silica layer and liquid metal core. The resonant frequencies of solid-SWM and liquid-RBM depend mainly on the physical parameters of the silica and liquid metal, respectively. These physical parameters are all related to the microcavity temperature, which can be electrically controlled by wiring the liquid metal to a circuit. The dissipative level attraction between the solid-SWM and liquid-RBM is achieved by changing the current applied to the liquid metal. Our results open new avenues toward exploring topological energy transfer between solid and liquid materials or ultrasensitive biological sensing around EPs.