In a very near future it is planned to base the International System of units (SI) on seven defining constants, among which are the Planck constant h and the elementary charge e. This modernization will allow the SI conform realizations of the electrical units, the volt and the ohm, from the Josephson effect and the quantum Hall effect, with unprecedented low uncertainties only limited by their implementation. This will benefit to measurements. Another advantage is that the ampere, once defined from e, can be realized using quantum effects, either by using single electron tunnelling devices or by applying directly Ohm’s law to the quantum voltage and resistance standards. In this context, LNE achieved to advance two quantum electrical standards.
We have developed graphene based quantum Hall resistance standards that can accurately operate in extended and significantly relaxed experimental conditions compared to state-of-the-art GaAs/AlGaAs devices [1,2]. These user-friendly and versatile quantum standards are compatible with broader industrial uses beyond those in National metrology Institutes.
More recently, we have developed a novel programmable quantum current generator (PQCG) by applying Ohm’s law in an original circuit [3] combining the Josephson voltage and quantum Hall resistance standards with a highly-accurate superconducting amplifier. We have demonstrated that currents generated in the milliampere are quantized in terms of efJ (fJ is the Josephson frequency) within one part in 108 [4]. Able to deliver currents down to the microampere range with such accuracies, the PQCG can be used to efficiently calibrate digital ammeters. Beyond, it brings a novel direct realization of the future definition of the ampere from the elementary charge with an uncertainty at the level of 1 part in 108 in the new SI. It therefore competes seriously with the electron pumps reaching only 2 parts in 107 at 90 pA [5] at the expense of big research efforts over the last two decades.
Moreover, the availability of graphene-based quantum resistance standards allows the implementation of the quantum voltage, resistance and current standards, as well as their combination, in a unique compact cryogen-free setup. This would constitute a major step towards the realization of a quantum multimeter based on the combination of the solid-state quantum effects.
[1] F. Lafont et al, Nat. Commun. 6, 6805 (2015).
[2] R. Ribeiro-Palau et al, Nat. Nanotech. 10, 965 (2015).
[3] W. Poirier et al, J. Appl. Phys. 115, 044509 (2014).
[4] J. Brun-Picard et al, Arxiv :1606.03964, under review (2016).
[5] F. Stein et al, Appl. Phys. Lett. 107, 103501 (2014).
Laboratoire national de métrologie et d’essais, Paris