Compact DC Josephson Voltage Standard

This paper presents precision measurements with a prototype cryogen-liquid-free DC Josephson voltage standard that produces a 1 V maximum output. Its cryostat is sufficiently compact that it can be operated on a bench close to devices under test. Compared to the National Institute of Standards and Technology (NIST) programmable Josephson voltage standard (PJVS), this bench-top Josephson voltage standard (BJVS) has a smaller cryostat (only 25 % of the volume), the Josephson junction array circuit is less complex and has only 10 % as many junctions, simpler bias electronics, and reduced mechanical cooling requirements. Direct voltage comparison between the BJVS and the PJVS achieved a relative agreement of 5×10^-10 at 1 V. With the recent redefinition of the International System of Units (SI), the BJVS becomes a primary realization the unit volt, requiring only access to a standard single-phase power outlet and a GPS signal (SI second).

I. Introduction

The dissemination of dc voltage from primary to secondary laboratories is nowadays exclusively dependent on the stability of Zener voltage standards. Although the uncertainty achieved with commercial Zener voltage standards is sufficient for most electrical instrument calibration, the intrinsic drift of Zener references requires their periodic calibration with a Josephson voltage standard (JVS) [1]. The Zener calibration with a PJVS is performed at a primary standards laboratory and requires shipping the Zener artifact. With the redefinition of International System of Units (SI), all Josephson voltage standards become a primary realization of the unit volt [2]. In this paper, we present a prototype of a simplified compact bench-top JVS (BJVS) designed to realize the unit volt. The maximum output voltage of the BJVS was chosen to be 1 V, but a small number of fixed voltages are realizable. The main advantages of the 1 V BJVS (Fig. 1) are the reduced complexity and cost of the bias electronics, higher fabrication yield of the BJVS array circuit (having fewer junctions than the 10 V programmable Josephson voltage standard (PJVS)), and the ability to run the cryogenic compressor from a standard single-phase power outlet. This more compact and easily deployable 1 V BJVS can realize the unit volt directly, such as at secondary standards laboratories, eliminating de facto multiple calibration measurements, typical of past traceability chains. The BJVS can also be implemented as a primary voltage reference for Kibble balances, which are now key instruments for the realization of the mass scale with the newly redefined SI, or as a traveling primary standard for interlaboratory comparisons. Fig. 1.

Cryocooled 1 V bench-top josephson voltage standard (air-cooled compressor not shown).