Thermomechanically squeezed multi-mode phonon lasers with levitated optomechanics.

Squeezing, an effective approach to reduce noise in one quadrature while increasing it in the orthogonal quadrature, has attracted broad attention to enhance the performance of mechanical oscillators in their thermal or ground states. However, the classical squeezing of phonon lasers, mechanical analogs of optical lasers, has not been achieved. Here, we report an experimental demonstration of a thermomechanically squeezed phonon laser with a microscale sphere in a levitated optomechanical system. Through non-adiabatic frequency shifts induced by a pulse-modulated trapping laser, the fundamental-mode phonon laser has been squeezed by 3.15 ± 0.35 dB. In such a way, we found that the second-harmonic mode of phonon lasers could be simultaneously squeezed, demonstrating the unique advantage of our system for concurrent coherent control of multi-mode phonon lasers. This work gives the first example of a squeezed nonlinear phonon laser with a larger mass under low vacuum, thus providing a promising platform for exploring nonlinear phononics and harnessing such a system for precision metrology.