Direct Comparison of Josephson Waveforms Using an AC Quantum Voltmeter

摘要

A new method for calibrating ac voltage waveforms based on measuring the difference relative to a synchronously synthesized waveform supplied from a programmable Josephson array is presented. In order to test the accuracy of this approach, the differences between two Josephson waveforms have been measured at the $pm$1.2-V level for frequencies up to 5 kHz. The uncertainties achieved are at least a factor of ten lower than those from the direct sampling method. Below 400 Hz, this new method gives an uncertainty of $5 times 10^{-8} (k = 1)$, while at 1 kHz, the uncertainty is about $2 times 10^{-7} (k = 1)$.