  Electron pumps generate a macroscopic electric current by controlled
manipulation of single electrons. Despite intensive research towards a quantum
current standard over the last 25 years, making a fast and accurate quantised
electron pump has proved extremely difficult. Here we demonstrate that the
accuracy of a semiconductor quantum dot pump can be dramatically improved by
using specially designed gate drive waveforms. Our pump can generate a current
of up to 150 pA, corresponding to almost a billion electrons per second, with
an experimentally demonstrated current accuracy better than 1.2 parts per
million (ppm) and strong evidence, based on fitting data to a model, that the
true accuracy is approaching 0.01 ppm. This type of pump is a promising
candidate for further development as a realisation of the SI base unit ampere,
following a re-definition of the ampere in terms of a fixed value of the
elementary charge.
