Rare Errors in a Well-Characterized Electron Pump: Comparison of Experiment and Theory

By measuring each junction of an electron pump in a single electron box configuration, we determine all quantities needed to test the standard theory of pumping error and leakage. Background charges are determined with an imprecision of ±0.01e. Electron temperature is measured to 40 mK. Measured charging energies show all junctions have nearly the same capacitance. We find agreement with theory at 140 mK, but a disagreement of many orders of magnitude at 40 mK. We suggest that the excess error and leakage at 40 mK are due to photon-assisted cotunneling processes not included in the standard theory.