Generating a thermal squeezed phonon laser via nonlinear optomechanical interaction

As a valuable resource of coherent phonons with high coherence, narrow linewidth, and strong intensity, phonon laser holds significant potential for advancing information storage, topology simulation, phonon time crystal, and high-precision acoustic sensing. Limited by the thermal fluctuations, generating a squeezed phonon laser remains challenging. We theoretically consider a cavity optomechanical system in an unresolved sideband regime. Remarkably, without any feedback control or detuning modulation, the thermal squeezed phonon laser could be generated through the nonlinear optomechanical interaction. Although in a large damping rate, the maximum thermal squeezing is available as the mechanical oscillator is driven toward dynamical instability. Our work unlocks an innovation platform to explore the coherent manipulation on a macroscopic scale, promoting the development of phonon-laser sensing technologies.