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Conference on Precision Electromagnetic Measurements

Comparison of the Programmable Quantum Current Generator and an Ultrastable Low-Noise Current Amplifier

Sophie Djordjevic, W. Poirier, D. Drung, Martin Götz

Published Aug 1, 2020• 2 citations
Publisher

Abstract

The 2019 revision of the International System of Units motivated different practical realizations of the ampere according to the corresponding Mise en pratique. Independently, the national metrology institutes of France and of Germany realized the unit ampere by using Ohm's law and practical realizations of volt and ohm by means of Josephson or quantum Hall effects, respectively. In this work, we present the results of the first direct comparison of both setups with the focus on currents at the level of 50 μA and 50 nA. The relative deviations are (4±3)×10-7and (14±6.5)×10-7respectively.

DOI
10.1109/cpem49742.2020.9191863

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The 2019 revision of the International System of Units motivated different practical realizations of the ampere according to the corresponding Mise en pratique. Independently, the national metrology institutes of France and of Germany realized the unit ampere by using Ohm's law and practical realizations of volt and ohm by means of Josephson or quantum Hall effects, respectively. In this work, we present the results of the first direct comparison of both setups with the focus on currents at the level of 50 μA and 50 nA. The relative deviations are (4±3)×10-7and (14±6.5)×10-7respectively.
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. Replacing the former definition based on Ampère's force law will allow one to fully benefit from quantum physics to realize the ampere.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.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.We demonstrate that currents generated in the milliampere range are accurately quantized in terms of ef J (f J is the Josephson frequency) with measurement uncertainty of 10 -8 .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.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.
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. Replacing the former definition based on Ampère's force law will allow one to fully benefit from quantum physics to realize the ampere.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.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.We demonstrate that currents generated in the milliampere range are accurately quantized in terms of ef J (f J is the Josephson frequency) with measurement uncertainty of 10 -8 .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.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.
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, ±(n/p)efJ, with relative uncertainties less than 10−8, where n and p are integer control parameters and fJ 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. Realizing the ampere, the unit of electrical current, involves controlling a flow of elementary charges with high accuracy. Here, the authors present the generation of sizeable currents at quantized values with relative uncertainties below 10−8.
We report on the development of a programmable quantum current generator (PQCG) based on quantum voltage and resistance standards. First measurements with a digital amperemeter in the 100 μA range demonstrate the linearity of the generated current as a function of the theoretical current, linked to the electron charge, with a relative uncertainty of 2.7 × 10-7(k = 1). To overcome the detector limits and validate the PQCG as a practical realization of the ampere in the new SI, accurate quantization measurements with a target combined uncertainty of a few parts in 108are in progress.
The design, fabrication, and the characterization of a 0.5-V Josephson junction array device are presented for the quantum voltage standards in the National Institute of Metrology (NIM) of China. The device consists of four junction arrays, each of which has 1200 3-stacked Nb/Nb x Si1−x /Nb junctions and an on-chip superconducting microwave circuit which is mainly a power divider enabling each Josephson array being loaded with an equal amount of microwave power. A direct current (dc) quantum voltage of about 0.5 V with a ∼1-mA current margin of the 1st quantum voltage step is obtained. To further prove the quality of NIM device, a comparison between the NIM device with the National Institute of Standards and Technology (NIST) programmable Josephson voltage standard (PJVS) system device is conducted. The difference of the reproduced 0.5-V quantum voltage between the two devices is about 0.55 nV, which indicates good agreement between the two devices. With the homemade device, we have realized a precise and applicable 0.5-V applicable-level quantum voltage.