  We introduce a hybrid tripartite quantum system for strong coupling between a
semiconductor spin, a mechanical phonon, and a microwave photon. Consisting of
a piezoelectric resonator with an integrated diamond strain concentrator, this
system achieves microwave-acoustic and spin-acoustic coupling rates $\sim$MHz
or greater, allowing for simultaneous ultra-high cooperativities ($\sim 10^3$
and $\sim 10^2$, respectively). From finite-element modeling and master
equation simulations, we estimate photon-to-spin quantum state transfer
fidelities exceeding 0.97 based on 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.
