Metrological Standards for Josephson Devices

Josephson devices exploit the quantum mechanical tunnelling of Cooper pairs across a superconducting junction to generate voltage steps that are directly linked to fundamental constants. Since the first demonstration of the Josephson effect in the 1960s, automated Josephson voltage standards (JVS) have formed the backbone of DC voltage metrology, establishing a direct traceability route to the Josephson constant and thereby to the SI unit of voltage. In recent decades, advances in microfabrication have permitted the integration of tens of thousands of junctions into series arrays, enabling programmable Josephson voltage standards (PJVS) to synthesize arbitrary waveforms and extend quantum standards into the AC regime. These developments have underpinned new approaches to precision calibration, from differential sampling methods that compare unknown signals against pulse-driven Josephson synthesised waveforms, to ac quantum voltmeters capable of covering audio and radio frequencies with uncertainties at the parts-in-10^8 level. Globally, national metrology institutes have adopted these quantum standards to disseminate ultra-stable voltage references, facilitate interlaboratory comparisons, and improve the accuracy of instrumentation in fields as diverse as power systems, telecommunications and particle accelerator control. Ongoing research focuses on enhancing the operational bandwidth, reducing uncertainty contributions such as phase jitter and sampling errors, and developing compact cryogenic systems for wider industrial deployment.

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Metrological Standards for Josephson Devices publication trend

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Technical terms

Josephson effect: The quantum tunnelling phenomenon in a superconducting junction that produces quantised voltage steps proportional to frequency.

Josephson voltage standard (JVS): A device using series arrays of superconducting junctions to generate a stable DC reference voltage with quantum-limited uncertainty.

Programmable Josephson voltage standard (PJVS): An arrangement of junction subarrays that can be selectively biased to synthesise arbitrary voltage waveforms linked to the Josephson constant.

AC quantum voltmeter (AC-QVM): A measurement instrument that utilises differential sampling against a Josephson-synthesised waveform to determine AC signal amplitudes with quantum-based traceability.

Differential sampling: A calibration method comparing an unknown signal and a reference waveform by synchronised digitisation to isolate voltage differences with high accuracy.

Traceability: The property of a measurement result whereby it can be related to stated references, typically national or international standards, through an unbroken chain of calibrations.

References

1. Differential Sampling of AC Waveforms Based on a Commercial Digital-to-Analog Converter for Reference. Sensors (2024).
2. Simulation Analysis of Phase Jitter in Differential Sampling of AC Waveforms Based on the Programmable Josephson Voltage Standard. Electronics (2024).
3. Josephson voltage standards as toolkit for precision metrological applications at PTB. Measurement Science and Technology (2022).
4. An AC quantum voltmeter for frequencies up to 100 kHz using sub-sampling. Metrologia (2021).