Progress toward a 1 V pulse-driven ac Josephson voltage standard

We present a new record output voltage of 275 mV rms, which is a 25 % improvement over the maximum achieved with previous ac Josephson voltage standard circuits. We demonstrate operating margins for these circuits and use them to measure the harmonic distortion of a commercial digitizer. Having exceeded the threshold of 125 mV rms for a single array of Josephson junctions, we propose an eight-array circuit capable of achieving 1 V rms.