Quantum squeezing induced nonreciprocal phonon laser

Phonon lasers or coherent amplifications of mechanical oscillations are powerful tools for fundamental studies on coherent acoustics and hold potential for diverse applications, ranging from ultrasensitive force sensing to phononic information processing. Here, we propose the use of an optomechanical resonator coupled to a nonlinear optical resonator for directional phonon lasing. We find that by pumping the nonlinear optical resonator, directional optical squeezing can occur along the pump direction. As a result, we can achieve the directional mechanical gain using directional optical squeezing, thereby leading to nonreciprocal phonon lasing with a well-tunable directional power threshold. Our work proposes a feasible way to build nonreciprocal phonon lasers with various nonlinear optical media, which are important for a wide range of applications, such as directional acoustic amplifiers, invisible sound sensing or imaging, and one-way phononic networks.