Piezoelectric Nanocavity Interface for Strong Coupling between a Superconducting Circuit, Phonon, and Spin

We introduce a hybrid tripartite quantum system for strong coupling between a semiconductor spin, a mechanical phonon, and a microwave excitation of a superconducting circuit. Consisting of a piezoelec-tric resonator with an integrated diamond strain concentrator, this system achieves microwave-acoustic and spin-acoustic coupling rates of approximately megahertz or greater, allowing simultaneous ultrahigh coop-erativities (approximately 103 and approximately 102, respectively). From finite-element modeling and master-equation simulations, we estimate superconducting-circuit-to-spin quantum state transfer fidelities exceeding 0.95 on the basis of separately demonstrated device parameters. We anticipate that this device will enable hybrid quantum architectures that leverage the advantages of both superconducting circuits and solid-state spins for information processing, memory, and networking.