Characterizing electromechanical coupling of dielectric materials for superconducting circuits*

To further improve the coherence time of superconducting qubits, one needs to consider many different sources of loss. Among those, dielectric loss has been studied in depth, and one contributor of this loss can originate from the electromechanical coupling between the superconducting circuit and the dielectric. In my talk, I will present a highly sensitive technique for measuring electromechanical coupling in a material at cryogenic temperatures and in the GHz regime. The measurement is based on RF driving of phonons through electromechanical coupling and optical readout through Brillouin scattering. I will show measurements done on various materials, including the observation of effective piezoelectricity in inversion symmetric materials, and discuss its implications for qubit coherence times.