  We show how superconductors can be used to couple, initialize, and read out
spatially separated spin qubits. When two single-electron quantum dots are
tunnel coupled to the same superconductor, the singlet component of the
two-electron state partially leaks into the superconductor via crossed Andreev
reflection. This induces a gate-controlled singlet-triplet splitting which,
with an appropriate superconductor geometry, remains large for dot separations
within the superconducting coherence length. Furthermore, we show that when two
double-dot singlet-triplet qubits are tunnel coupled to a superconductor with
finite charging energy, crossed Andreev reflection enables a strong two-qubit
coupling over distances much larger than the coherence length.
