A practical device for 1 nV accuracy measurements in Josephson arrays

A reference voltage source for measurements of the electromotive force (EMF) of standard cells is presented. The device is easy to operate and is perfectly safe for standard cells. It measures the EMF of a standard cell with respect to the array voltage with a precision of 0.4 nV within a run; run-to-run variations of the cell EMF of +or-2 nV are observed over a 17-d period. However, to obtain these results the cell must be sufficiently stable and the temperature fluctuations must not exceed about 10 mu K during the measurement.<
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