Point-Contact Josephson Voltage Standard

This paper describes a practical Josephson voltage standard used to calibrate transfer standard cells. The standard comprises a niobium point-contact Josephson junction-used as the voltage reference-and a series-parallel combination voltage divider. The construction of this Josephson junction is quite unique, and it is robust. It withstands temperature cycling between room temperature and 4.2 K. The point contact is adjusted at room temperature. The output of the point-contact Josephson junction at 4.2 K with a 9.59-GHz microwave signal applied is about 1.9 mV. The divider ratio is 1/529, and divider ratio stability is better than 0.2 ppm/year at room temperature. Our point-contact Josephson junction was compared with the tunnel junction used to determine the Japanese standard volt. The difference between the two was less than 0.5 ppm.