What is Quantum in Quantum Pumping: The role of the Phase and Asymmetries

By studying several examples, we show that quantum pumping does not always necessitate a strictly quantum description, neither is phase always a necessary concept. The same quantum mechanical picture of pumping encompass a variety of distinct mechanisms, some can be simulated by classical mechanisms while others can be explained only in a quantum picture; the role of the phase of the wavefunction is the crucial differentiator. We also show that most pumping processes have a previously unconsidered antisymmetric component which contributes significantly to the instantaneous current at each terminal but causes no net charge transfer . We have also computed the exact pumped current for arbitrary rates of time variation for certain potentials, not just in the adiabatic regime as has been previously studied.