  Electrically addressing spin systems is predicted to be a key component in
developing scalable semiconductor-based quantum processing architectures, to
enable fast spin qubit manipulation and long-distance entanglement via
microwave photons. However, single spins have no electric dipole, and therefore
a spin-orbit mechanism must be integrated in the qubit design. Here, we propose
to couple microwave photons to atomically precise donor spin qubit devices in
silicon using the hyperfine interaction intrinsic to donor systems and an
electrically-induced spin-orbit coupling. We characterise a one-electron system
bound to a tunnel-coupled donor pair (1P-1P) using the tight-binding method,
and then estimate the spin-photon coupling achievable under realistic
assumptions. We address the recent experiments on double quantum dots (DQDs) in
silicon and indicate the differences between DQD and 1P-1P systems. Our
analysis shows that it is possible to achieve strong spin-photon coupling in
1P-1P systems in realistic device conditions without the need for an external
magnetic field gradient.
