Cryocooled Josephson standards for AC voltage metrology

P Durandetto,E Monticone,B Trinchera,V Lacquaniti,A Sosso,M Fretto

doi:10.1088/1742-6596/841/1/012031

Abstract

The Josephson effect is worldwide used as a basis for constant reference voltages in national metrological institutes and in calibration laboratories of industry. Research on Josephson voltage standards is aiming at a fundamental change also in the metrology of the volt for AC and arbitrary waveforms: programmable Josephson voltage standards converting a digital code into a quantum-accurate stepwise waveform are already available in primary laboratories and even more advanced standards for converting sub-nanosecond binary coded pulses into any arbitrary signal with quantum accuracy are now actively developed and tested. A new experimental setup based on a two-stage Gifford-McMahon cryocooler has been developed at INRiM for the operation of AC-Josephson voltage standards. Among its distinct features, the possibility of employing both the aforementioned techniques (programmable and pulsed Josephson voltage standards) is particularly interesting. Quantum-based AC voltage sine waves have been synthesized with both programmable and pulse-driven arrays, although their accuracy is still limited by thermal oscillations due to the cryocooler piston motion.

Highlights

The application of superconducting devices based on Josephson effect for the synthesis of AC voltage waveforms has been investigated for many years
The flatness of voltage steps was determined under microwave radiation by recording the current-voltage (IV ) characteristics of all the PJVS subarrays and was deduced by a linear fit within 100 μA of current operating margins: for the entire array (8192 junctions) we obtained 0.8 μV/μA at 1.28 V and 0.4 μV/μA at 2.56 V. These results suggest the use of these quantized voltage steps for synthesis of stepwise sine waves
We have demonstrated the feasibility of synthesizing quantum-based sine waves in the kHz range with the two different techniques presented here

Summary

Introduction

The application of superconducting devices based on Josephson effect for the synthesis of AC voltage waveforms has been investigated for many years. Arrays of many thousands of Josephson junctions for DC voltage standards are, to date, among the most important achievements of superconducting electronics. The main techniques employed for the generation of quantum-based waveforms are programmable and pulse-driven AC-JVSs. Programmable arrays are subdivided in sub-circuits with series-connected junctions to generate voltages following a power of 2-sequence (1, 2, 4, 8, 16, ...). Cryogen-free operation of JVSs is regarded as crucial to widen the range of applications of quantum standards, due to its greater ease of use with respect to liquid helium and for possible shortages and high cost of the latter. In this paper we present last results obtained with both programmable and pulse-driven Josephson standards in cryocooler setup

Measurement setup

Results

Conclusion