  Nanoscale single-electron pumps can be used to generate accurate currents,
and can potentially serve to realize a new standard of electrical current based
on elementary charge. Here, we use a silicon-based quantum dot with tunable
tunnel barriers as an accurate source of quantized current. The charge transfer
accuracy of our pump can be dramatically enhanced by controlling the
electrostatic confinement of the dot using purposely engineered gate
electrodes. Improvements in the operational robustness, as well as suppression
of non-adiabatic transitions that reduce pumping accuracy, are achieved via
small adjustments of the gate voltages. We can produce an output current in
excess of 80 pA with experimentally determined relative uncertainty below 50
parts per million.
