High-Accuracy Josephson Potentiometer

A potentiometer with the extremely small relative uncertainty of a few parts in 109 has been developed by utilizing the property that a Josephson junction generates a precise voltage that is variable with frequency and step number. The evaluated total uncertainty is 2.5 × 10-9V for measurements at the 1-V level. This small uncertainty is attributed to the generation of a higher than normal Josephson voltage, that is, on the order of 100 mV.