  The adiabatic pumped current through an unbiased one dimensional (1D)
channel, connected to two 1D leads and subject to surface acoustic waves (SAW),
is calculated exactly for non-interacting electrons. For a broad range of the
parameters, quantum interference generates a staircase structure of the
time-averaged current, similar to experimental observations. This corresponds
to integer values (in units of electronic charge) of the charge pumped during
each period of the SAW. We also find staircases for higher harmonics. Quantum
interference can thus replace Coulomb blockade in explaining the pumped charge
quantization, particularly in the SAW experiments.
