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First BIPM-NMIJ direct comparison of PJVSs at 10 V based on different technologies

The BIPM's new transportable programmable Josephson voltage standard (PJVS) was used for the first time for an on-site comparison, at the NMIJ (Japan), in December 2015.

During this work, and for the first time, the NMIJ Josephson junction technology (niobium nitride (NbN)-based junctions) operated on a Gifford-McMahon cryocooler at 10 K was directly compared to the NIST Josephson junction technology (amorphous niobium silicon NbxSi1-x junctions) cooled down in liquid helium. The recent computation of the results shows that nominally identical voltages produced by both systems agreed to within 5 × 10−12 (0.05 nV) at the level of 10 V DC.

A large number of the experiments performed during the comparison were devoted to investigating the impact of a multi-stage filter installed at the output measurement leads of the primary standards. The capacitance parameters of the filter have a strong impact on the width of the Shapiro quantum voltage step and on the amplitude of a systematic voltage error. Filtering the output of the voltage leads of the PJVS has the positive consequence of increasing the width of the quantum voltage step. On the other hand, the leakage resistance of the capacitances will increase the systematic error due to the voltage drop, which also depends on the number of capacitors across the measurement leads.

If care is not taken, the voltage error can be larger than the voltage difference between the two quantum standards by two orders of magnitude.

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