Precision measurements of AC Josephson voltage standard operating margins

Recent advances in circuit design and fabrication of superconducting integrated circuits have enabled us to demonstrate an ac Josephson voltage standard (ACJVS) that generates both ac and dc waveforms up to 242-mV peak voltage. Using a Fast Fourier Transform spectrum analyzer and an ac-dc transfer standard, we characterize ACJVS operating margins by performing "flat-spot" measurements at the level of a part in 10⁶ for all eight bias parameters. By verifying that every bias parameter has a "flat-spot" (i.e., a range of bias values over which the measured ACJVS output is precisely constant), we demonstrate that all Josephson junctions on the chip are operating properly.