  We propose a new implementation of a universal set of one- and two-qubit
gates for quantum computation using the spin states of coupled single-electron
quantum dots. Desired operations are effected by the gating of the tunneling
barrier between neighboring dots. Several measures of the gate quality are
computed within a newly derived spin master equation incorporating decoherence
caused by a prototypical magnetic environment. Dot-array experiments which
would provide an initial demonstration of the desired non-equilibrium spin
dynamics are proposed.
