Cryogenic ac Josephson Effect emf Standard Using a Superconducting Current Comparator

Abstract

A cryogenic ac Josephson effect emf standard has been developed in which all precise measurements are carried out in a superfluid helium bath. This standard uses a superconducting current comparator having a ratio accuracy of better than 1 in 109 for the calibration of a resistive potential divider. The cryogenic emf standard has a precision of 1.1 in 108 and corroborates the results obtained from an ac Josephson effect standard using conventional room temperature techniques.

An overview of some of CSIRO’s “Underground Science” capabilities

“…This early work contributed significantly to the refinement in the value of the constant 2 e/ h. CSIRO also contributed significantly to the field of metrology via the invention of the superconducting a e-mail: keith.leslie@csiro.au This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly cited. cryogenic current comparator, a device that allows the ratio of currents to be determined with accuracies of order a few parts in 10 10 [1].…”

SQUIDs for Standards and Metrology

“…The early work on the CCC described in the next section was aimed at Josephson voltage measurements, using cryogenic resistors to scale the voltage to higher levels [18,19]. In the 1970s, the primary voltage standards were indeed based on single overdamped Josephson junctions which generated a voltage of only a few millivolts (typically working on high-order steps, n > 500 at frequency f » 10 GHz).…”

Precision high-value resistance scaling with a two-terminal cryogenic current comparator

“…12,13 Early two-terminal CCC systems were developed in the 1970s to compare cryogenic resistors used in voltage ratio dividers. 14,15 These bridges could measure large resistance ratios and allowed low-voltage Josephson standards consisting of only a few junctions to be compared to 1.018 V standard Weston cells for precise voltage metrology. They were displaced by Josephson junction arrays 16 that did not require voltage scaling and later restored for use in the measurement of small currents based on the QHR.…”