“…At the present time, the most practically useful combination of accuracy and high electron pumping rate has been achieved using electrostatically gated semiconductor quantum dots (QDs) operated as non-adiabatic tunable-barrier pumps [3] in the low-temperature decay cascade regime [4]. Using state-of-the-art current measurement techniques [5,6], there have been several reports of pumped current accurate at the part-per-million (ppm) level or better, at pump repetition rates in the range 0.5 GHz f 1 ⩽ ⩽ GHz, generating current 80 pA = I ef 160 P ⩽ ⩽ pA [5,[7][8][9][10][11], where e is the elementary charge. These studies were performed on a variety of device architectures: etch-defined [5,8,10] and gate-defined [7] QDs in GaAs heterostructures, and silicon nano-wire MOSFETs [9].…”