  While traditionally considered a deleterious effect in quantum dot spin
qubits, the spin-orbit interaction is recently being revisited as it allows for
rapid coherent control by on-chip AC electric fields. For electrons in bulk
silicon, SOC is intrinsically weak, however, it can be enhanced at surfaces and
interfaces, or through atomic placement. Here we show that the strength of the
spin-orbit coupling can be locally enhanced by more than two orders of
magnitude in the manybody wave functions of multi-donor quantum dots compared
to a single donor, reaching strengths so far only reported for holes or
two-donor system with certain symmetry. Our findings may provide a pathway
towards all-electrical control of donor-bound spins in silicon using electric
dipole spin resonance (EDSR).
