Direct comparison of a 1 V Josephson arbitrary waveform synthesizer and an ac quantum voltmeter

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 108. Sources for systematic errors have been investigated. The overall uncertainty is found to be better than 1.2 parts in 108 (k = 1) for measurements at a frequency of 250 Hz and 1 V amplitude.