Towards a quantum representation of the ampere using single electron   pumps
  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. 
S. P. Giblin, M. Kataoka, J. D. Fletcher, P. See, T. J. B. M. Janssen,   J. P. Griffiths, G. A. C. Jones, I. Farrer, D. A. R...
cond-mat.mes-hall physics.ins-det