Laboratory voltage standard based on 2e/h

The increased dependence of a standards laboratory on a stable voltage reference has made the maintenance of a “volt” by standard cells a costly and time consuming process. This paper describes an instrument designed to calibrate cadmium-sulfate standard cells directly against a time-invariant superconducting Josephson junction voltage reference, thus replacing the large groups of cells typically used as a voltage reference. An induced voltage of 5.2 mV is produced across the Josephson junction by irradiating the junction with microwaves of a known frequency. A specially designed potentiometer is used to scale this voltage up to 1.01+ V where it can be compared to a standard cell. The overall accuracy (2 σ) of the system is 0.4 ppm or better.