  Experimental studies of spin transport in a two-dimensional electron gas
hosted by a triple GaAs/AlGaAs quantum well are reported. Using time-resolved
Kerr rotation, we observed the precession of the spin polarization about a
current-controlled spin-orbit magnetic field. Spatially-resolved imaging showed
a large variation of the electron g-factor and the drift transport of coherent
electron spins over distances exceeding half-millimetre in a direction
transverse to the electric field.
