Accuracy evaluation and mechanism crossover of single-electron transfer in Si tunable-barrier turnstiles

Abstract

Using an error-counting scheme, we evaluated the accuracy of single-electron (SE) transfer in Si tunable-barrier turnstiles in a dilution refrigerator. The error counting was performed by shuttling SEs between a lead and a charge-accumulating node and detecting in real time the number of electrons in the node with an SE-resolution charge sensor. The best experimentally obtained error rate is about 100 parts per million (ppm), where the SE capture in the SE island occurs in thermal equilibrium due to the heating effect on SEs caused by pulse voltages applied to modulate the potential barrier. When we reduce the heating effect by suppressing the pulse voltages, there is a change in the SE transfer mechanism to nonequilibrium SE capture. We theoretically discuss the crossover point of the change. Moreover, at the minimum pulse voltage, the theoretical lower bound of the error rate estimated by fitting is on the order of 0.01 ppm. This suggests that Si SE-transfer devices are promising candidates for use as quantum current standards in metrology.