Cryocooled Programmable and Pulse-driven Josephson Voltage Standards at INRiM

In the last decades, voltage metrology research has been mainly directed towards the application of arrays of Josephson junctions for the synthesis of quantum-based ac and arbitrary voltage waveforms. Currently, ac voltage calibrations are performed with conventional calorimetric methods based on ac-dc transfer standards, but they are not intrinsically accurate. Programmable and pulse-driven Josephson arrays represent the two more common ways for linking ac voltage calibrations to a quantum phenomenon. Moreover, in order to allow the spread of Josephson standards in many industries and laboratories, a user-friendly and safe refrigeration system is preferable: cryocoolers satisfy these needs. In this work, we present our cryocooler system for the operation of ac Josephson voltage standards. We synthesized sine waves at different amplitudes in the kHz range with both programmable and pulsed standards. In order to guarantee a proper operation, optimal thermalization of the Josephson chip is required and interventions aimed at this goal are presented here.