Accurate measurement of currents generated by single electrons transported in a one-dimensional channel

The acoustoelectric current generated by the transport of single electrons using surface acoustic waves through a one-dimensional channel offers the possibility of realising a quantum standard of current based on the electronic charge e. At NPL a measurement system using a commercial electrometer has been developed for investigating the flatness and accuracy of the constant current plateaux with an uncertainty of 15fA. Also a new instrument, based on a cryogenic current comparator (CCC), has been developed with which it is expected that a relative accuracy of 1fA/nA can be achieved. The authors present preliminary measurements of the quantised current using the electrometer and an experimental arrangement for resolving the 'metrological triangle' using the CCC.