Progress in the establishment of a Josephson voltage standard at NPL, India

This paper describes the progress made at the National Physical Laboratory (NPL), India in establishing a voltage standard based on the ac Josephson effect. A voltage standard at 1-mV level using a Nb-Nb point contact junction has been established and the as-maintained volt based on a bank of standard cells has been intercom-pared against it using a 1:1000 voltage divider. The experimental setup used in this comparison and results of recent measurements are described. The as-maintained volt has been found to agree with the Josephson voltage (using the value of 2e/h − 48 3594.0 GHz/V) within 0.5 ppm.