EMRP - REUNIAM: Redefinition of the SI base unit ampere

• Forschungsstelle: METAS
• Projektnummer: 5211.08.FP.065
• Projekttitel Englisch: EMRP - REUNIAM: Redefinition of the SI base unit ampere

Schlüsselwörter (Englisch)

Primary capacitance standard, quantum metrology, electricity, single electron effect

Kurzbeschreibung (Englisch)

For the last two decades, quantum metrology has been a very active research field. The Josephson and the quantum Hall effect are now well established quantum effects on which the dc voltage and dc resistance scales are based. However, new and challenging developments are now underway:

• The quantum Hall is envisioned as a new ac standard of resistance which will soon serve as a primary standards for the impedance scale.
• Manipulations of single electrons made possible the generation of small electrical currents with a metrological accuracy. Such experiments open up the possibility to realise current and capacitance standards.

On a more fundamental ground, these experiments will allow to verify the consistency of the metrological triangle. The metrological triangle is closed in the following way: a cryo-capacitor is charged electron by electron and its voltage is measured in terms of the Josephson effect. This gives one determination of the capacitance. Then the value of the capacitor is compared to the AC-QHE using a quadrature bridge which is actually under development. This last step closes the metrological triangle. This important experiment -in addition to the development of a primary standard of capacitance- represents a good test of the consistency of the electrical unit within the SI.

The primary capacitance standard consists of an electron pump coupled to an single elctron tunneling (SET) electrometer allowing the measurement of the pump current electron by electron. This device is then used to load a cryo-capacitor electron by electron up to a voltage of 10 V. This voltage is compared to the output of a Josephson voltage standard. This allows to express the value of the capacitance as a function of e and K-J90.

This project is partly funded by the European Community’s Seventh Framework Programme, ERA-NET Plus under Grant Agreement No 217257.

Projektziele (Englisch)

Close the metrological triangle with a total uncertainty smaller than 10^-7.

Abstract (Englisch)

The set-up necessary to operate single electronic devices and to close the metrological triangle with the required accuracy was successfully completed and tested. Cryogenic measurements of a standalone SET electrometer have revealed clear Coulomb oscillations showing that the measurement setup is fully operational. However, measurements performed at cryogenic temperature using a design where the electrometer is coupled to the electron pump were never successful. Despite particular care during the mounting and measurement, the problem of sample fragility, in particular with the electrometer, remained with these samples. Due to the fragility of the SET devices, the closure of the metrological triangle was not achieved within the project. An another attempt with a new sample design is the subject of another project.
Another part of the project was to establish the traceability for the cryo-capacitor measurement. To this end, a capacitance comparison has been included in the project (EURAMET.EM-S31). Therefore, the whole R-C chain had to be characterized and the calibration of 10 pF capacitance standard in terms of RK-90 was realized with an uncertainty of about 0.1 µF/F (k=1).

Umsetzung und Anwendungen (Englisch)

The main outcome for METAS in the project is the improvement of the capacitance chain (based on the quantized Hall resistance) and of the related measurement and calibration services.

Publikationen / Ergebnisse (Englisch)

A. Rüfenacht, B. Jeanneret and S. V. Lotkhov, “Electron Counting Capacitance Standard: Progress Report”, Poster presentation at the Conference on Precision Electromagnetic Measurements (CPEM), Daejeon, 13-18 June 2010, Conference Digest pp. 291 (2010)