Linearity of quantized voltages generated by a Josephson-junction array

A measurement system is proposed to examine experimentally the linearity of quantized voltages generated by a Josephson-junction array at 100 MV and 1 V with an accuracy better than 1*10/sup -8/. Ten resistors, connected in series, are driven by a constant-current source and the total voltage drop is compared with the sum of the voltages across each resistor. A preliminary experiment at the 0.2-p.p.m. level was performed. The main cause of the lower accuracy than expected was the instability of the junction array's voltages, which seems to be attributable to imperfect cryostat design.<
>