Advances toward high-accuracy operation of tunable-barrier single-hole pumps in silicon

Precise and reproducible current generation is the key to realizing quantum current standards in metrology. A promising candidate is a tunable-barrier single-charge pump, which can accurately transfer single charges one by one with an error rate below the ppm level. Although several measurements have shown such levels of accuracy, it is necessary to further pursue the possibility of high-precision operation toward reproducible generation of the pumping current in many devices. Here, we investigated silicon single-hole pumps, which may have the potential to outperform single-electron pumps because of the heavy effective mass of holes. Measurements on the temperature dependence of the current generated by the single-hole pump revealed that the tunnel barrier had high energy selectivity, which is a critical parameter for high-accuracy operation. In addition, we applied the dynamic gate-compensation technique to the single-hole pump and confirmed that it yielded a further performance improvement. Finally, we demonstrated gigahertz operation of a single-hole pump in which the estimated lower bound of the pump error rate was around 0.01 ppm. These results imply that single-hole pumps in silicon are capable of high-accuracy, high-speed, and stable single-charge pumping in metrological and quantum-device applications.