The role of quantum interference and asymmetries in the operation of quantum pumps

Quantum pumping is a means of generating current in mesoscopic circuits without a bias field. We show that within a common quantum theoretical description, the phenomenon of quantum pumping encompasses fundamentally different processes. Some of them can be explained with classical physics, but others rely on quantum interference for operation. We identify and explain their quantum versus classical origins. For a class of quantum pumps we derive exact analytical expressions for the pumped current that applies at arbitrary operation frequency from adiabatic to non-adiabatic. We show that the pumped current often contains a hidden, and even dominant, antisymmetric component that does not contribute to net transfer in a period.