Controlling the error mechanism in a tunable-barrier nonadiabatic charge pump by dynamic gate compensation

Single-electron pumps based on tunable-barrier quantum dots are the most promising candidates for a direct realization of the unit ampere in the recently revised International System of Units (SI): they are simple to operate and show high precision at high operation frequencies. The current understanding of the residual transfer errors at low temperature is based on the evaluation of back-tunneling effects in the decay cascade model. This model predicts a strong dependence on the ratio of the time-dependent changes in the quantum dot energy and the tunneling barrier transparency. Here we employ a two-gate operation scheme to verify this prediction and demonstrate control of the back-tunneling error. We derive and experimentally verify a quantitative prediction for the error suppression, thereby confirming the basic assumptions of the back-tunneling (decay cascade) model. Furthermore, we demonstrate a controlled transition from the back-tunneling dominated regime into the thermal (sudden decoupling) error regime. The suppression of transfer errors by several orders of magnitude at zero magnetic field was additionally verified by a sub-ppm precision measurement.