22 years of quantum Hall effect metrology

Summary form only given. This talk will be a review of the history of quantum Hall effect metrology from a personal point of view since I had the chance to participate in this history from the beginning. At CPEM 80 von Klitzing introduced his discovery to the metrological community. The question arose, if there is a possible metrological application. Consequently in the early eighties a lot of effort was put into the availability of suitable samples and into experiments, which had been characterized mainly by decreasing the measurement uncertainty, by the search for the best values for the characteristic constant and by clarifying if it might be possible to detect any deviation from the quantization. It was the time when the international co-operation between the metrological institutes in this field started to become very intensive. At the CPEM held in Tsukuba in 1988 a working group of the CCE reviewed critically the experiments available at that time and stated a draft for a recommendation to applicate the quantum Hall effect for the maintenance of the ohm. Through the official bodies of the metre convention this recommendation became effective on January 1st, 1990. All national metrological institutes follow this recommendation since that date. In the meantime this procedure has been established very successfully. The BIPM has built a transportable quantum Hall effect measurement system and has performed up to now at several NMIs bilateral comparisons in calibrating resistances. They show that the results in the calibrations do not differ more than the uncertainties of the set-ups, which have reached a few parts in a billion. Stimulated by this great success in the maintenance of the ohm the desire among metrologists is great to develop a similar procedure for the maintenance of an ac quantity, the farad. Therefore a great effort is put at several institutes into the experimental investigation of the quantum Hall effect with alternating currents in the kHz rang- . Although the experimental effort is much higher compared to dc measurements, the results indicate that a similar application will be possible.