  We investigate charge pumping in carbon nanotube quantum dots driven by the
electric field of a surface acoustic wave. We find that at small driving
amplitudes, the pumped current reverses polarity as the conductance is tuned
through a Coulomb blockade peak using a gate electrode. We study the behavior
as a function of wave amplitude, frequency and direction and develop a model in
which our results can be understood as resulting from adiabatic charge
redistribution between the leads and quantum dots on the nanotube.
