  Spin-$\frac{1}{2}$ $^{119}$Sn nuclei in a silicon semiconductor could make
excellent qubits. Nuclear spins in silicon are known to have long coherence
times. Tin is isoelectronic with silicon, so we expect electrons can easily
shuttle from one Sn atom to another to propagate quantum information via a
hyperfine interaction that we predict, from all-electron linearized augmented
plane wave density functional theory calculations, to be roughly ten times
larger than intrinsic $^{29}$Si. A hyperfine-induced electro-nuclear
controlled-phase (e-n-CPhase) gate operation, generated (up to local rotations)
by merely holding an electron at a sweet-spot of maximum hyperfine strength for
a specific duration of time, is predicted to be exceptionally resilient to
charge/voltage noise. Diabatic spin flips are suppressed with a modest magnetic
field ($>15~$mT for $<10^{-6}$ flip probabilities) and nuclear spin bath noise
may be avoided via isotopic enrichment or mitigated using dynamical decoupling
or through monitoring and compensation. Combined with magnetic resonance
control, this operation enables universal quantum computation.
