Towards a He-Free Source of Arbitrary Quantum Voltage Signals

The Josephson effect is worldwide exploited as the basis for constant reference voltages in National Metrological Institutes (NMIs) and in industry calibration laboratories. Lately, voltage metrology research has been mainly directed towards the application of Josephson effect for the synthesis of very accurate ac and arbitrary voltage signals: pulse-driven Josephson arrays represent the most promising way for linking ac voltage calibrations to a quantum phenomenon. Furthermore, an easy and secure cooling system based on cryocoolers is desirable in order to allow the spread of Josephson standards outside NMIs. A Gifford-McMahon cryocooler is currently in use at INRiM for the operation of ac-Josephson Voltage Standards (JVSs). We employed pulse-driven JVSs for synthesizing sine waves with frequency in the kHz range and amplitudes in the mV range, with distortion around 80 dBc. In this report we present a detailed description of this technique and of the refrigeration system employed.