Although the electrical current is usually described by a flow of elementary charges per second, the definition of the ampere, unit of electrical current in the International System of units (SI), is still based on an electromechanical force expressed in newtons. This definition set in 1948 limits the accuracy of electrical measurements and of derived quantities. A major overhaul, planned in 2018, aims at put SI units in line with modern physics to reduce measurement uncertainties, by fixing the value of certain fundamental constants, among them the elementary charge that will be used to define the ampere. In 2016, researchers from the Laboratoire national de métrologie et d’essais (LNE) developed a quantum current standard, universal and practical, able to generate for the first time, currents of values in a range from microampere to milliampere that are accurately linked to the elementary charge with the targeted relative uncertainty of 10 parts in a billion.
This breakthrough relies on an error-free application of the Ohm’s law to the highly-accurate quantum standards of resistance and voltage, based on two macroscopic quantum effects only linked to fundamental constants, the quantum Hall effect and the Josephson effect, occurring in two-dimensional semiconductors and superconductors respectively.
This novel quantum current generator improves the accuracy of current standards by two orders of magnitude and paves the way to fully quantum-based electrical measurements in the SI.
This research was published in the Physical Review X (PRX) journal of the American Physical Society (APS): J. Brun-Picard, S. Djordjevic, D. Leprat, F. Schopfer and W. Poirier, "Practical Quantum Realization of the Ampere from the Elementary Charge", Phys. Rev. X, 6, 041051 (2016).
It was also covered by a Viewpoint commentary "A New Era for the Ampere", in the on-line Physics journal of the APS.
A French team of researchers based at National Metrology and Testing Laboratory (LNE) and various laboratories at National Center for Scientific Research (CNRS) has found that graphene, which led to the 2010 Nobel Prize in Physics, can be used to realize a primary standard of electrical resistance based on the quantum Hall effect, which operates with state-of-the-art accuracy and in experimental conditions much more practical than that required by conventional semiconductors.
These results, published in Nature Nanotechnology on 7 September 2015, pave the way to a broader use of the universal and accurate quantum electrical standards to the benefit of Science and Industry. They also contribute to the redefinition of the International System of units, including the redefinition of the kilogram. Moreover, they proof that graphene is now mature for a very demanding application.
Preliminary works were published in Nature Communications in April 2015 (Nat. Commun. 6, 6806 (2015)).
Research groups involved :
This research received funding from the French Agence Nationale de la Recherche (ANR), and was partly supported within the European Metrology Research Programme (EMRP) project SIB51, GraphOhm.
Publication: R. Ribeiro-Palau, F. Lafont, J. Brun-Picard, D. Kazazis, A. Michon, F. Cheynis, O. Couturaud, C. Consejo, B. Jouault, W. Poirier and F. Schopfer « Quantum Hall resistance standard in graphene devices under relaxed experimental conditions » paru dans Nature Nanotechnology le 7 Septembre 2015. http://dx.doi.org/10.1038/nnano.2015.192
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