Coherent transport by adiabatic pumping - An application to electrons in a quantum dot coupled to a superconducting lead

We derive a general scattering-matrix formula for the pumped current through a coherent mesoscopic region attached to a normal and a superconducting lead. As an application of this result we calculate the current pumped through a quantum dot coupled to a superconducting lead. Andreev reflection is shown to enhance the pumped current by up to a factor of 4 in case of equal coupling to the leads. We find that this enhancement can still be further increased for slightly asymmetric coupling and show that the pumping cycle is completed well before decoherence sets in. Adiabatic pumping of electrons can thus in principle be used to coherently transfer quantum information across a quantum dot structure.