![]() (a) Illustration of the two ways to generate a current from the frequency f ( s − 1 ) and the elementary charge e, expressed in amperes in the future SI. Practical realization of the ampere from quantum electrical effects. ![]() Our work improves the accuracy of current standards by 2 orders of magnitude and paves the way for fully quantum-based electrical measurements that will benefit the new SI system. We show that the generated currents are quantized in terms of e f J-the Josephson frequency-with uncertainties of only 10 parts in one billion. Our novel quantum current generator accordingly benefits from the high level of universality and reproducibility of these two quantum standards, which are based on macroscopic quantum phenomena only linked to the Planck constant and the elementary charge e. ![]() This breakthrough relies on the programmable amplification of the quantized current obtained from an accurate application of Ohm’s law to the programmable quantum Josephson voltage standard and the quantum Hall resistance standard combined in an original quantum circuit. Here, we report on a programmable quantum current generator delivering quantized currents that range from 1 μ A to 5 mA, directly linked to e. However, a highly accurate quantum realization of the ampere is still missing despite many efforts to develop quantum devices handling electrons one by one. A major overhaul is planned in 2018 to put SI units in line with modern physics by fixing the values of some fundamental constants, among them the elementary charge e, which will define the ampere. This definition, set in 1948, limits the accuracy of electrical measurements in SI units. In addition, it opens the way to further developments in metrology and in fundamental physics, such as a quantum multimeter or new accurate comparisons to single-electron pumps.Īlthough electrical current can be described by the flow of elementary charges per second, the ampere is still defined in the International System of Units (SI) from an electromechanical force occurring between current-carrying wires, explained by Ampère’s force law. This new quantum current source, which is able to deliver such accurate currents down to the microampere range, can greatly improve the current measurement traceability, as demonstrated with the calibrations of digital ammeters. ![]() We demonstrate that currents generated in the milliampere range are accurately quantized in terms of e f J ( f J is the Josephson frequency) with measurement uncertainty of 10 − 8. Starting again with Ohm’s law, applied here in a quantum circuit combining the quantum Hall resistance and Josephson voltage standards with a superconducting cryogenic amplifier, we report on a practical and universal programmable quantum current generator. However, a quantum realization of the ampere from e, accurate to within 10 − 8 in relative value and fulfilling traceability needs, is still missing despite the many efforts made for the development of single-electron tunneling devices. Replacing the former definition based on Ampère’s force law will allow one to fully benefit from quantum physics to realize the ampere. One major change of the future revision of the International System of Units is a new definition of the ampere based on the elementary charge e.
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