  The manipulation of single spins in double quantum dots by making use of the
exchange interaction and a highly inhomogeneous magnetic field was discussed in
[W. A. Coish and D. Loss, Phys. Rev. B 75, 161302 (2007)]. However, such large
inhomogeneity is difficult to achieve through the slanting field of a
micromagnet in current designs of lateral double dots. Therefore, we examine an
analogous spin manipulation scheme directly applicable to realistic GaAs double
dot setups. We estimate that typical gate times, realized at the
singlet-triplet anticrossing induced by the inhomogeneous micromagnet field,
can be a few nanoseconds. We discuss the optimization of initialization,
read-out, and single-spin gates through suitable choices of detuning pulses and
an improved geometry. We also examine the effect of nuclear dephasing and
charge noise. The latter induces fluctuations of both detuning and tunneling
amplitude. Our results suggest that this scheme is a promising approach for the
realization of fast single-spin operations.
