Generation of AC waveforms using a NbN-based programmable Josephson voltage standard system with a 10-K cooler

We are developing a system for precise AC waveform synthesis in a frequency range below kilo-hertz using a programmable Josephson voltage standard (PJVS). Our PJVS circuit is composed of 65 536 NbN-based over-damped Josephson junctions and operated at a temperature of 9-10 K with a mechanical cooler. We succeeded in generating stepwise-approximated sinusoidal waveforms with peek voltage amplitude of 2 V using a 10-bit PJVS circuit and a bias source with twelve 12-bit digital-to-analog converters. Rough estimations suggest the transient time between each step in the obtained waveforms is less than 5 μs, sufficient for sampling measurements.