Direct DC Voltages Comparison between two Programmable Josephson Voltage Standards at SCL

Standards and Calibration Laboratory (SCL) setup in 2018 a liquid helium based programmable Josephson voltage standard (PJVS) developed by the National Institute of Standards and Technology (NIST). The system was validated by direct comparison with a NIST transportable PJVS system at 1.018 V, 4 V, 6 V, 8 V and 10 V. The difference between the systems was within 0.5 nV, with an expanded uncertainty of less than 2.2 nV ( k=2). In this paper, the setup and the results of the direct comparison method are presented.