Josephson voltage standards as toolkit for precision metrological applications at PTB

Abstract

60 years after the discovery of the Josephson effect, electrical DC voltage calibrations are routinely performed worldwide - mostly using automated Josephson voltage standards (JVS). Nevertheless, the field of electrical quantum voltage metrology is still propagating towards AC applications. In the past 10 years the fabrication of highly integrated arrays containing more than 50 000 or even 300 000 junctions has achieved a very robust level providing highly functional devices. Such reliable Josephson arrays are the basis for many novel applications mainly focussing on precision ac measurements for signal frequencies up to 500 kHz. Two versions of quantum AC standards are being employed. Programmable Josephson voltage standards (PJVS), based on series arrays divided into subarrays, reach amplitudes up to 20 V and usually are used as quantum voltage reference in measurement systems. Pulse driven arrays reach amplitudes up to 1 V or even 4 V and are typically used as Josephson arbitrary waveform synthesizers (JAWS). This paper summarizes the principal contributions from PTB to the present state of Josephson voltage standards with particular focus on developments for precision metrological applications and our proof-of-concept demonstrations.

A Voltage Monitoring Approach for Eliminating Flux Trapping in Josephson Junction Arrays

“…Programmable Josephson junction arrays [1][2][3][4][5][6][7] are superconducting integrated circuits that operate at a low temperature of 4.2 K. External electromagnetic and thermal disturbances can lead to trapped magnetic ux in these kinds of devices [8][9][10][11]. This results in the localized trapping of quantized magnetic ux [12][13][14][15][16][17][18], which can suppress the critical current of the Josephson junction, thereby affecting its normal operation [22][23][24][25].…”

Critical Temperature and Critical Current Enhancement in Arrays of Josephson Junctions: A Ginzburg–Landau Perspective

“…Research on these arrays was also motivated by the rather successful operation of the quantum voltage standard, both in superconductor-isolator-superconductor (SIS) junctions' [22][23][24] and in superconductornormal-superconductor (SNS) junctions' [25,26] operation modes. Nowadays, arrays of Josephson junctions and related voltage standard chips are being used for relevant implementations of high-precision metrology [27]. From a fundamental point of view, 2D arrays have served as a benchmark for testing solid-state phase transitions [28][29][30][31][32][33] and the coherent generation of microwave and millimeter-wave radiation [34][35][36][37][38][39][40][41].…”

Wideband AC Voltage Standards

“…In recent years, the improvement of the JVS is focused on improving the operation of the cryocoolers, which enable signi-ficant reduction of usage of expensive liquid helium [18,19], increasing the amplitude of the generated voltage by up to 20 V by increasing the number of Josephson junctions in the arrays (even up to 300 000) [20] and reducing the harmonics in the output signal developed from the Josephson arbitrary voltage synthesizer (JAWS) [21].…”