Topological phonon transport in an optomechanical system

Recent advances in cavity-optomechanics have now made it possible to use light to measure mechanical motion down to the individual phonons. At the same time, microfabrication techniques have enabled small-scale on-chip optomechanical circuits. Motivated by these developments, several theoretical works have envisioned larger scale optomechanical systems where light is used to steer and detect on-chip topological vibrations. We present the observation of topological phonon transport within a multiscale optomechanical crystal structure consisting of an array of over 800 cavity-optomechanical elements. Using sensitive, spatially resolved optical read-out, we detect thermal phonons in a 0.325−0.34 GHz band traveling along a topological edge channel, with substantial reduction in backscattering. This work further advances the ongoing effort to miniaturize topological phononic devices down to the nanoscale, opening the way to GHz frequency acoustic wave circuits comprising robust delay lines and non-reciprocal elements.