Leakage and counting errors in a seven-junction electron pump

Leakage and counting errors are explored experimentally in a well-character ized seven-junction electron pump and compared with predictions of the orth odox theory, including cotunneling. Theory and experiment are in good agree ment at intermediate temperatures, where errors are dominated by thermally activated, single-junction processes. At low temperatures, however, the obs erved errors far exceed predictions, indicating that the orthodox theory om its an important error process.