Cavity enhanced piezo-optomechanical coupling to a bulk crystalline resonator.

We report the observation of cavity enhanced photon-phonon interactions between a 3D microwave cavity mode and a bulk mechanical resonator mediated by piezoelectric and radiation pressure effects. The system is composed of a quartz bulk acoustic wave resonator placed inside a microwave re-entrant cavity. The cavity mode photonic field is modulated by a 5 MHz bulk acoustic wave shear mode, which is modeled and experimentally verified through the input-output formalism. Through finite element method simulations, we show the potential of the system to reach high cooperativities and perform coherent signal processing. The device presented represents an important step towards realising enhanced sensitivity for applications ranging from sensing to quantum information science including the study of macroscopic quantum mechanics.