  Spin currents in channels of a high mobility GaAs/AlGaAs two-dimensional
electron gas are generated and detected using spin-polarized quantum point
contacts. We have recently shown that the relaxation length of spin currents is
resonantly suppressed when the frequency at which electrons bounce between
channel walls matches the Larmor frequency. Here we demonstrate that a gate on
top of the channel tunes such ballistic spin resonance by tuning the velocity
of electrons and hence the bouncing frequency. These findings demonstrate a new
mechanism for electrical control of spin logic circuits.
