Experimental Test of the Josephson Frequency-Voltage Relation

The Josephson frequency-voltage relation in superconduction's $\nu =\frac{2eV}{h}$ has been tested by measuring frequency-voltage ratios in Josephson junctions using three different Josephson-effect phenomena: (1) microwave emission from evaporated-film tunnel junctions, (2) microwave-induced quantum voltages in evaporated-film tunnel junctions, and (3) microwave-induced current steps in the $I-V$ characteristics of evaporated-film tunnel junctions and of "weak-link" point-contact junctions. The use of the "harmonic effects" associated with each phenomenon to increase the accuracy of measurement, and the factors limiting the accuracy in each case, are discussed. The measured frequency-voltage ratios for the three methods were the same to within their respective experimental errors. The highest accuracy was obtained using microwave-induced current steps. The measured frequency-voltage ratio in this case was equal to the currently accepted value of $\frac{2e}{h}$ to within an experimental accuracy of 0.006% (60 ppm). The frequency-voltage ratio was also found to be independent of the type of junction used, temperature, magnetic field, harmonic number, voltage polarity, microwave power, and frequency to within the 10-ppm precision of the measurements.