Coherent acoustic frequency comb via floquet engineering of optical tweezer phonon lasers.

Floquet engineering, featuring time-periodic control of various systems, has enabled observations of many exotic phenomena such as time crystals, breaking of reciprocity symmetry, and exceptional topology. Theoretically, a periodic drive can make the system inherit the time period and generate new harmonics or distort the band structure at the fundamental frequency. Here, by combining such a technique with levitated optomechanics, we present an instructive example of a coherent acoustic frequency comb with microsphere phonon lasers. This work shows that our technique offers the capability of flexibly controlling both the teeth number and the teeth spacing of the resulting coherent acoustic frequency comb. In particular, we confirm that all Floquet-driven comb teeth can reach the truly coherent regime, i.e., satisfying all the characteristic features of phonon lasers. Our work provides a platform to drive the nonlinear phonon laser to a coherent acoustic frequency comb with truly coherent comb teeth.