Hidden quantum pump effects in quantum coherent rings -: art. no. 075303

Time periodic perturbations of an electron system on a ring are examined. For small frequencies, periodic small amplitude perturbations give rise to sideband currents which, in leading order, are inversely proportional to the frequency. These sideband currents compensate the current of the central band such that to leading order, no net pumped current is generated. In the nonadiabatic limit, larger pump frequencies can lead to resonant excitations: as a consequence, a net pumped current arises. We illustrate our results for a one-channel ring with a quantum dot whose barriers are modulated parametrically.