  A dc current can be pumped through a nanostructure by two out-of-phase ac
driving fields. In this approach, we explore the pumped current properties
driven by square-wave, sawtooth-wave, and triangle-wave ac fields in nanowire
structures by Fourier expansion. The theory can be applied to arbitrary driving
fields. It is found that the pumped current varies with the phase difference as
square-wave and sawtooth-wave functions, respectively, under corresponding
driven fields. The sinusoidal relation governs in the pump driven by
triangle-wave oscillation. Devices based on square-wave driven quantum pumps
may have potential applications in digital information at nanoscale dimensions.
