  Direct interactions between quantum particles naturally fall off with
distance. For future-proof qubit architectures, however, it is important to
avail of interaction mechanisms on different length scales. In this work, we
utilize a superconducting resonator to facilitate a coherent interaction
between two semiconductor spin qubits 250 $\mu$m apart. This separation is
several orders of magnitude larger than for the commonly employed direct
interaction mechanisms in this platform. We operate the system in a regime
where the resonator mediates a spin-spin coupling through virtual photons. We
report anti-phase oscillations of the populations of the two spins with
controllable frequency. The observations are consistent with iSWAP oscillations
and ten nanosecond entangling operations. These results hold promise for
scalable networks of spin qubit modules on a chip.
