J. Kivioja, A. Niskanen, J. Pekola
Metrological standards of two of the important electrical quantities, voltage and resistance, are based on quantum devices operating at low temperatures. Voltage is defined through the Josephson effect and resistance through the quantum Hall effect. What is missing is the modern standard of electric current, which would thus complete the metrological triangle and pose a critical test on one of the fundamental constants of nature, h, the Planck’s constant. There have been attempts to realise a charge pump by applying periodic gate potentials to single-electron tunnelling arrays, and to Josephson junction arrays, and by applying an acoustic wave to trap single electrons in a travelling potential through a narrow semiconducting channel. The first of these methods suffers from very low yield: maximum currents are just few picoamperes, which is far too small to be applied in metrology. Josephson pumps can produce larger current, but up to now they have suffered from leakage current, which is a consequence of macroscopic quantum coherence in superconductors. The acoustic pump yields a high enough current but accuracy is rather poor presumably due to local heating in the conducting channel. We have recently proposed and performed the first experiments on a new type of a superconducting charge pump, which combines the high speed (current) and low leakage by making benefit of the techniques presently employed in manipulations of Josephson junction based quantum bits. This is a joint effort between LTL and VTT Information Technology.