  Recent experiments with silicon qubits demonstrated strong coupling of a
microwave resonator to the spin of a single electron in a double quantum dot,
opening up the possibility of long-range spin-spin interactions. We present our
theoretical calculation of effective interactions between distant quantum dot
spins coupled by a resonator, and propose a protocol for fast, high-fidelity
two-qubit gates consistent with experimentally demonstrated capabilities. Our
simulations show that, in the presence of noise, spin-spin entangling gates
significantly outperform cavity-mediated gates on charge qubits.
