  A dipolar gate alternative to the exchange gate based Kane quantum computer
is proposed where the qubits are electron spins of shallow group V donors in
silicon. Residual exchange coupling is treated as gate error amenable to
quantum error correction, removing the stringent requirements on donor
positioning characteristic of all silicon exchange-based implementations [B.
Koiller et al., Phys. Rev. Lett. 88, 027903 (2002)]. Contrary to common
speculation, such a scheme is scalable with no overhead in gating time even
though it is based on long-range dipolar inter-qubit coupling.
