The new BIPM 1-V reference standard based on an array of Josephson junctions

The authors report the first measurements at the Bureau International des Poids et Mesures (BIPM) with a 1-V reference standard based on an array of Josephson junctions. A novel procedure for standard cell measurements is described. It allows the measurement of a cell electromotive force (EMF) with a random uncertainty of less than 1 nV and a total uncertainty of about 2 nV while avoiding direct connection of the cell to the array. Comparisons with an older Josephson reference standard, which is based on a junction output of 10 mV, were made both indirectly by means of standard cells and directly by connecting the instruments together. The results and the random uncertainties imply that the value assigned to a standard cell using the array minus that given by the older apparatus is -18.8±3.4 nV for the indirect method and -17.1±1.5 nV for the direct method. Taking into account the estimated total uncertainty of 23.5 nV for the old system, the agreement is excellent