An ac quantum voltmeter based on a 10 V programmable Josephson array that is simple to use, provides dc and ac calibration up to kHz range for equipment widely used in metrology, and ensures direct traceability to a quantum-based standard, is developed. This ac quantum voltmeter is proven to match conventional Josephson standard systems at dc and extends its advantages up to 10 kHz in the low-frequency ac range. The ac quantum voltmeter is capable of performing calibrations up to 7 V RMS in the frequency range from dc to 10 kHz completely under software control. A direct comparison at dc has demonstrated an uncertainty better than 2 parts in 10 10 (k = 2). The uncertainty at 1 kHz is better than 1.7 µV V −1 (k = 2) for a measurement time of 1 min. The ac quantum voltmeter is a robust and practical system that fulfils the needs of general metrology laboratories for quantum-based voltage calibrations.
This paper describes the development of an automated ac quantum voltmeter toward a turnkey system, which can be used for calibration of common dc and ac voltage standards. The setup was tested in an accredited commercial calibration laboratory to characterize Fluke 5700A calibrators and voltage standards. The measured voltage in dependence on various parameters is presented in the range of dc to 2 kHz with amplitudes up to 10 V. The uncertainty components are discussed, and the system relevant Type B uncertainty for ac voltage calibrations is 0.15 µV/V. The contribution of the leakage current is investigated in detail and found to be notable for frequencies above 1 kHz due to parasitic capacitances. The combined measurement uncertainty for calibration ac voltages is less than 0.62 µV/V (k = 1 and 40 Hz-1 kHz) and is limited by the noise of the calibrator. Comparison measurements at Physikalisch-Technische Bundesanstalt have been done and confirm the system reproducibility.Index Terms-AC Josephson metrology, ac quantum voltmeter, calibration, calibrator Fluke 5700A, Josephson voltage standard, programmable Josephson voltage standard (PJVS).
We present the connection of two programmable Josephson arrays generating synchronous waveforms to measure impedance ratios—the Josephson two-terminal-pair impedance bridge. This approach is more flexible than conventional bridges at the same level of uncertainty. The Josephson bridge can measure over a wider frequency range, over a wider range of impedance ratios than conventional two-terminal-pair bridges. Furthermore, the phase angle between the two impedances can take any value. As a first application, we present measurements of a 1 : 1 resistance ratio at the 10 kΩ level in the frequency range between 25 Hz and 10 kHz. The uncertainties are better than a few parts in 108 and hence comparable to those of conventional impedance bridges. Quantization at up to 10 kHz was confirmed by varying the bias current of the Josephson arrays, resulting in constant resistance ratios within the measurement resolution.
AC Josephson voltage standards based on pulse-driven Josephson arrays (Josephson arbitrary waveform synthesizer-JAWS) have recently achieved an output voltage of at least 1 V root-mean-square. An ac quantum voltmeter (ac-QVM) based on a 2 V programmable Josephson array has been used to verify the quantization level of the new JAWS by performing a direct comparison in the frequency range from 30 Hz to 2 kHz. The comparison has demonstrated an excellent agreement between the two quantum standards of better than 1 part in 10 8 . Sources for systematic errors have been investigated. The overall uncertainty is found to be better than 1.2 parts in 10 8 (k = 1) for measurements at a frequency of 250 Hz and 1 V amplitude.
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