AC Josephson Effect Determination of e/h: A Standard of Electrochemical Potential Based on Macroscopic Quantum Phase Coherence in Superconductors

Abstract : An ac Josephson effect determination of e/h with significantly improved accuracy is reported. The precision of the measurement is determined by uncertainties associated with the comparison of a Josephson device voltage with the emf of an electrochemical standard cell voltage reference and is about 3 parts in 10 to the 8th power. This precision was made possible by use of Josephson devices at voltages above 10 mV and design and construction of two special voltage comparator instruments. The fabrication and operation of the Josephson devices and the design and performance of the voltage comparators are discussed.