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Quantum-generated “high” voltage

Programmable Josephson voltage standard up to 80 volts

PTBnews 2.2023
Especially interesting for

metrology institutes

electrical quantum metrology

fundamental research

Programmable Josephson voltage standards are electrical quantum standards consisting of series arrays with several thousand Josephson junctions. They typically allow the generation of voltages up to 10 volts with fundamental accuracy and are mainly used by national metrology institutes for the realization of the electrical voltage unit. PTB has now succeeded in realizing the world’s first output voltages of up to 80 volts with a Josephson voltage standard.

Photo of two 20 V Josephson arrays mounted on a sample holder. Two further arrays are mounted on the lower surface.

This development was motivated by the requirements of an experiment for fundamental research in atomic physics conducted at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg. Penning traps use magnetic and electrostatic fields to store ions and require ultra-stable and low-noise voltage sources. The MPIK’s PENTATRAP mass spectrometer is used to determine mass ratios of heavy, long-lived and highly charged ions. The five Penning traps in PENTATRAP use a highly stable conventional voltage source up to 90 volts developed in-house. Despite its high temporal stability, the voltage source limits the achievable relative measurement uncertainty to approximately 10−11. For further improvement, MPIK and PTB are collaborating to develop a highly stable quantum voltage source based on the Josephson voltage standard. The required increase in output voltage, from the typical 10 volts of (widespread) Josephson voltage standards, poses special challenges for the connection of the arrays in a compact system that incorporates the microwave and current needed by the arrays.

An output voltage of about 80 volts has now been successfully generated at PTB by connecting four 20-volt Josephson arrays in series. This voltage level represents a world record in terms of Josephson voltage standards. In the first studies to validate the system, two sets of two arrays operated in series were compared with each other at PTB and a relative agreement of better than 10−9 was determined.

In an initial test at the PENTATRAP experiment at a voltage of about 22 volts, the Josephson voltage source has already improved the temporal stability by a factor of three. Also here, an increase of the voltage level up to 80 volts is planned. In addition, an electronic bias source is currently being developed to allow the simple, programmable adjustment of the output voltage over the entire voltage range.


Luis Palafox
Department 2.6, Electrical Quantum Metrology
Phone: +49 531 592-2140
Opens local program for sending emailluis.palafox(at)ptb.de

Scientific publication

L. Palafox, R. Behr, F. Müller: Programmable Josephson Voltage Standard up to 80 V. 2022 Conference on Precision Electromagnetic Measurements (CPEM), Wellington, New Zealand, December 2022, 493–494