Circuit quantum acousto-dynamics with bulk acoustic wave resonators

High overtone bulk acoustic wave resonators (HBAR) are one of the newest mechanical platformsto have reached the quantum regime during the past years. Making use of the high frequency, lowloss phonon modes of the HBAR, these systems potentially enable the study of macroscopic quantumobjects with long coherence times and relatively large effective masses. Therefore, a hybrid systemconsisting of superconducting circuit qubits strongly coupled to modes of a HBAR is an excitingnew system for studying hardware-efficient quantum memories, Heisenberg-limited force sensing,and objective collapse theories.
As steps toward realizing these possibilities, we present our work on improving the performanceof HBAR-based circuit quantum acousto-dynamics devices. We approach this crucial task fromseveral directions by studying the effect of new materials, geometries, and fabrication methods onthe quantum coherence, coupling strength, and acoustic mode structure of the system. We then usethese next-generation devices to demonstrate quantum control of phonons in the HBAR.