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.
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.
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.
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 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.
Electrical quantum metrology using superconducting circuits relies on phase synchronization effects of Josephson oscillations with ac signals, resulting in equidistant voltage steps and forming the basis of today’s voltage standards. Because charge and phase are conjugate variables, the dual effect of equidistant current steps should also exist and was indeed predicted theoretically. It relies on so-called Bloch oscillations, which are oscillations of voltage occurring when a current-biased Josephson junction is embedded in an environment with characteristic impedance larger than the superconducting resistance quantum h/4e^2. In addition, Josephson junctions of lateral size on the order of tens of nm are necessary, such that their Josephson and charging energy are approximately equal. Synchronizing such Bloch-oscillations with an ac signal completes the duality with Shapiro steps, and results in the occurrence of steps in IV-measurements at I=2ef with e being the elementary charge, and f the frequency of the external ac signal. To emphasize the duality with Shapiro (voltage) steps, such current steps are called dual-Shapiro steps. Together with the established standards for voltage and resistance, a new standard for current based on dual-Shapiro steps would relate the ampere, volt and ohm through fundamental constants and frequency. If successfully realized with metrological precision this would close the quantum metrological triangle and might even enable the combination of all three electric quantum relations in one single device. Here we show our efforts towards the realization of quantized currents with metrological applicability. Based on advances in fabrication technology and measurement capabilities, we demonstrate quantized current steps up to I≈2 nA by synchronizing Bloch oscillations with external ac signals up to 6 GHz [1,2]. In addition, we demonstrate a pulsed driving scheme resulting in an asymmetric pattern of dual-Shapiro steps featuring increased differential resistance [2]. Finally, we discuss the effects limiting the precision of our quantized current steps and present our efforts for tackling them. [1] F. Kaap et al., “Synchronization of Bloch Oscillations in a Strongly Coupled Pair of Small Josephson Junctions: Evidence for a Shapiro-like Current Step,“ Phys. Rev. Lett. 132, 027001, 2024. [2] F. Kaap et al., “Demonstration of dual Shapiro steps in small Josephson junctions,“ Nature Communications 15, 8726, 2024.
The quantum Josephson voltage standard is well established across the metrology community for many years. It relies on the synchronization of the flux tunneling in the S/I/S Josephson junctions (JJ) with the microwave radiation (MW) of frequency f such that V=Φ0fm, where m = 0, 1, 2, …. The phenomenon is called the Shapiro steps. Together with the quantum Hall resistance standard, the voltage standard forms the foundation of electrostatic metrology. The current is then defined as the ratio of the voltage and resistance. Realization of the quantum current standard would close the electrostatic metrological triangle of voltage–resistance–current. The current quantization I=2efm, the inverse Shapiro steps, was recently shown using the superconducting nanowires and small JJ. The effect is a synchronization of the MW with the Cooper pair tunneling. This paves the way to combine the JJ voltage and current standards on the same chip and demonstrate feasibility of the multi-standard operation. We show the voltage and current quantization on the same chip up to frequency of 10 GHz, corresponding to the amplitudes ∼ 20.67 μV and ∼ 3.2 nA, respectively. The accuracy of the voltage and current quantization, however, is relatively low, 35 and 100 ppk, respectively. We discuss measures to optimize the JJs, circuit, and environment to boost the amplitude and accuracy of the standards.