Validation of a quantized-current source with 0.2 ppm uncertainty

We report on high-accuracy measurements of quantized current, sourced by a tunable-barrier single-electron pump at frequencies \(f\) up to \(1\) GHz. The measurements were performed with a new picoammeter instrument, traceable to the Josephson and quantum Hall effects. Current quantization according to \(I=ef\) with \(e\) the elementary charge was confirmed at \(f=545\) MHz with a total relative uncertainty of 0.2 ppm, improving the state of the art by about a factor of 5. For the first time, the accuracy of a possible future quantum current standard based on single-electron transport was experimentally validated to be better than the best realization of the ampere within the present SI.