Electron transport by a potential minimum that moves through a barrier is i
nvestigated numerically and theoretically. The integrated electron transfer
as a function of the Fermi level has a series of plateaus, each of which c
orresponds to an integral number of electrons. The accuracy of the quantiza
tion depends on the barrier height and can be 1 part in 10(10) or better. T
he transport mechanism involves nonadiabatic Landau-Zener transitions.