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We report on the performance of a 1-V dc programmable Josephson voltage standard (PJVS) operating on a commercially available Gifford-McMahon cryocooler at 4 K. The NIST-fabricated niobium superconductor-normal metal-superconductor junction chip has been shown to operate successfully as integrated with this cryopackage, generating 1.229 V at the maximum operating frequency of 19.364 GHz with Shapiro steps at constant voltage that are flat to within less than 100 nV. Because of the large operating margin (greater than 1 mA), these steps were highly stable and immune from noise. Differences in behavior of the PJVS in liquid helium and on the cryocooler are discussed. This demonstration paves the way towards automated warming and cooling of the Josephson device and a fully automated voltage standard system. [ABSTRACT FROM AUTHOR]

A custom-designed laboratory prototype of a four-stage Stirling-type pulse tube cryocooler was recently developed by Lockheed Martin for niobium integrated circuits (ICs) operating close to 4 K. Basic system performance has been verified by integration with a Nb IC test chip, with cells that include a high-speed rapid single flux quantum (RSFQ) binary counter. For 650 W total compressor power, extended stable operation of the counter at T = 4.5 K was demonstrated with a clock frequency up to 46 GHz, with 25 mW of excess cooling capacity on the coldest stage. The thermodynamic, electromagnetic, and mechanical performance are promising for the development of an improved compact cryocooler for practical superconducting electronic applications in fields such as wireless communications. [ABSTRACT FROM AUTHOR]