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We have evaluated the linearity of commercial digital voltmeters (DVMs) using a programmable Josephson voltage standard (PJVS) system. The PJVS system is composed of a 524 288-niobium nitride-based Josephson junction array that has the ability to generate arbitrary output voltages up to 17 V with a resolution of 12 bits. In our system, the junction array is operated in a 10-K compact cooler without a liquid-helium coolant. Up to now, we have succeeded in generating accurate dc voltage levels of up to approximately 13 V using this system. In this paper, we demonstrate our PJVS system as a tool for investigating the linearity characteristics of commercial DVMs, with an accuracy level of 0.1 \mu \textV /V or better, and discuss the uncertainty sources in these measurements. [ABSTRACT FROM PUBLISHER]

We precisely evaluated a single-chip 10-V programmable Josephson voltage standard (PJVS) system based on a closed-cycle refrigerator by directly comparing it with a conventional Josephson voltage standard system. The PJVS chip fabricated using NbN/TiNx/NbN junction technology was used. The result of the measurement showed a good agreement with a combined standard uncertainty of 3.1 parts in 1010 at 10 V. [ABSTRACT FROM AUTHOR]

We report the experimental results on a Josephson junction array (JJA) driven by current pulse trains generated by triggering a photo detector located in a cryostat with an optical comb. The key components in the experimental system are a mode locked fiber laser, a metal-semiconductor-metal (MSM) photoconductive switch, and an overdamped JJA. Optical pulse trains generated at room temperature are transmitted via an optical fiber to the MSM-photo detector installed at 4.2 K, and then converted into electric current pulse trains to drive the overdamped JJA. Quantized voltage steps have been verified at multiples of 10 μV, which agrees with the repetition rate of the pulse laser and the number of Josephson junctions in the JJA. [ABSTRACT FROM AUTHOR]