Two NIST Programmable Josephson Voltage Standard (PJVS) systems have been directly compared at 10V using different nanovoltmeters at the temperature of the laboratory. These PJVS systems use arrays double-stacked superconducting-niobium Josephson junctions with barriers made of niobium-silicide. Compared to the voltages produced by conventional Josephson voltage standards, PJVS systems produce intrinsically stable quantum-accurate voltages. However, in order to guarantee the quantization of the voltages and to characterize the errors at the room-temperature voltage output of the probe, a number of additional precautions need to be followed. We report several experimental results that have significant systematic errors that generate voltages that appear reproducible but are, in fact, inaccurate. When the proper measurement procedures are followed, the results of a direct comparison using an analog detector show that the two independent PJVS systems can agree, relatively, within 2.6 parts in 10^11 with a total combined uncertainty of 4.5 parts in 10^11 (k=1). Investigations to characterize the leakage resistance of each PJVS to ground show that its contribution to the uncertainty budget is among the most significant.
Pub Type: Journals
Digital-analog conversion, Josephson arrays, Quantization, Standards, Superconducting integrated circuits, Voltage measurement