Josephson Arbitrary Waveform Synthesizer as a Reference Standard for the Calibration of Lock-in Amplifiers

We have extended the voltage range of the Josephson arbitrary waveform synthesizer from 1 mV down to $1\ \mu\mathrm{V}$ at frequencies from 60 Hz to 1 kHz to calibrate precision lock-in amplifiers. Experimental results show that the system's uncertainty is dominated by the resolution of the lock-in amplifier. We anticipate that the Josephson arbitrary waveform synthesizer-based system will extend the lower voltage and frequency range of ac voltage metrology and improve the uncertainties by one order of magnitude compared to conventional techniques.