Counting electrons one by one-overview of a joint European research project

The European COUNT project exploits two complementary single electron tunneling devices for use in electrical current metrology: a single electron pump as a current source and a single electron counter as a current meter. An electron pump has been developed with on-chip resistors in order to suppress cotunneling. The intended accuracy is 1 ppm for a current of a few picoamperes. Apart from being a quantum current standard, the electron pump could also be the basis of a capacitance standard. A coaxial tunable cryogenic capacitor of 1 picofarad has been developed for this purpose. A passive electron counter based on a single electron transistor embedded in a resonant tank circuit has been further investigated and developed in order to reach both high sensitivity and high counting speed. The intended accuracy is 10 ppm for a current of a few picoamperes.