Title: Engineering phonon leakage in nanomechanical resonators,
Abstract: We propose and experimentally demonstrate a technique for coupling phonons
out of an optomechanical crystal cavity. By designing a perturbation that
breaks a symmetry in the elastic structure, we selectively induce phonon
leakage without affecting the optical properties. It is shown experimentally
via cryogenic measurements that the proposed cavity perturbation causes loss of
phonons into mechanical waves on the surface of silicon, while leaving photon
lifetimes unaffected. This demonstrates that phonon leakage can be engineered
in on-chip optomechanical systems. We experimentally observe large fluctuations
in leakage rates that we attribute to fabrication disorder and verify this
using simulations. Our technique opens the way to engineering more complex
on-chip phonon networks utilizing guided mechanical waves to connect quantum
systems.