A primary quantum current standard based on the Josephson and the quantum Hall effects

The new definition of the ampere calls for a quantum current standard able to deliver a flow of elementary charges, $e$, controlled with a relative uncertainty of $10^{-8}$. Despite many efforts, nanodevices handling electrons one by one have never demonstrated such an accuracy for a net flow. The alternative route based on applying Ohm's law to the Josephson voltage and quantum Hall standards recently reached the target uncertainty in the milliampere range, but this was at the expense of the application of error corrections. Here, we present a new programmable quantum current generator, which combines both quantum standards and a superconducting cryogenic amplifier in a quantum electrical circuit enabling the current scaling without errors. Thanks to a full quantum instrumentation, we demonstrate the accuracy of the generated currents, in the microampere range, at quantized values, $\pm(n/p)ef_\mathrm{J}$, with relative uncertainties less than $10^{-8}$, where $n$ and $p$ are integer control parameters and $f_\mathrm{J}$ is the Josephson frequency. This experiment sets the basis of a universal quantum realization of the electrical units, for example able of improving high-value resistance measurements and bridging the gap with other quantum current sources.