Phase-controlled phonon laser

A phase-controlled ultralow-threshold phonon laser is proposed by using tunable optical amplifiers in coupled-cavity-optomechanical system. The multiplicative behavior of the individual enhancements, by engineering the phases and strengths of external parametric driving, makes it possible to achieve the strong-coupling regime of optomechanics, where the switching among radiation-pressure, parametric amplification, and three-mode optomechanical couplings can be realized and ultralow-threshold phonon lasing is observable. This opens up novel prospects for applications in, e.g. quantum acoustics, nonlinear phonon devices, and ultrasensitive motion sensing.