  Pumping of electrons through nano-scale devices is one of the fascinating
achievements in the field of nano-science with a wide range of applications. To
optimize the performance of pumps, operating them at high frequencies is
mandatory. We consider the influence of fast periodic driving on the average
charge transferred through a quantum dot. We show that it is possible to
reverse the average current by sweeping the driving frequency only. In
connection with this, we observe a rectification of the average current for
high frequencies. Since both effects are very robust, as corroborated by
analytical results for harmonic driving, they offer a new way of controlling
electron pumps.
