  We introduce a method for high-fidelity quantum state transduction between a
superconducting microwave qubit and the ground state spin system of a
solid-state artificial atom, mediated via an acoustic bus connected by
piezoelectric transducers. Applied to present-day experimental parameters for
superconducting circuit qubits and diamond silicon vacancy centers in an
optimized phononic cavity, we estimate quantum state transduction with fidelity
exceeding 99\% at a MHz-scale bandwidth. By combining the complementary
strengths of superconducting circuit quantum computing and artificial atoms,
the hybrid architecture provides high-fidelity qubit gates with long-lived
quantum memory, high-fidelity measurement, large qubit number, reconfigurable
qubit connectivity, and high-fidelity state and gate teleportation through
optical quantum networks.
