  Single-electron transport driven by surface acoustic waves (SAW) through a
narrow constriction, formed in two-dimensional electron gas, is studied
theoretically. Due to long-range Coulomb interaction, the tunneling coupling
between the electron gas and the moving minimum of the SAW-induced potential
rapidly decays with time. As a result, nonadiabaticiy sets a limit for the
accuracy of the quantization of acoustoelectric current.
