We report on high-accuracy measurements of quantized current, sourced by a tunable-barrier single-electron pump at frequencies f up to 1 GHz. The measurements were performed with a new picoammeter instrument, traceable to the Josephson and quantum Hall effects. Current quantization according to I = ef with e the elementary charge was confirmed at f = 545 MHz with a total relative uncertainty of 0.2 ppm, improving the state of the art by about a factor of 5. For the first time, the accuracy of a possible future quantum current standard based on single-electron transport was experimentally validated to be better than the best realization of the ampere within the present SI.
We report on characterizations of single-electron pumps at the highest accuracy level, enabled by improvements of the small-current measurement technique. With these improvements a new accuracy record in measurements on single-electron pumps is demonstrated: 0.16 µA • A −1 of relative combined uncertainty was reached within less than 1 d of measurement time. Additionally, robustness tests of pump operation on a sub-ppm level revealed a good stability of tunable-barrier single-electron pumps against variations in the operating parameters.
In the quantum anomalous Hall effect, the edge states of a ferromagnetically doped topological insulator exhibit quantized Hall resistance and dissipationless transport at zero magnetic field. Up to now, however, the resistance was experimentally assessed with standard transport measurement techniques which are difficult to trace to the von-Klitzing constant RK with high precision. Here, we present a metrologically comprehensive measurement, including a full uncertainty budget, of the resistance quantization of V-doped (Bi,Sb)2Te3 devices without external magnetic field. We established as a new upper limit for a potential deviation of the quantized anomalous Hall resistance from RK a value of 0.26 ± 0.22 ppm, the smallest and most precise value reported to date. This provides another major step towards realization of the zero-field quantum resistance standard which in combination with Josephson effect will provide the universal quantum units standard in the future.Quantum standards are the backbone of the system of measurement units. Already since 1990 all electrical units are based on flux quantization in units of ℎ 2 ⁄ , realized with the Josephson effect [1,2], and conductance quantization in units of 2 ℎ ⁄ , realized with the quantized Hall effect (QHE) [3,4]. With the revision of the international system of units, SI, in near future [5,6] also the realizations of the units of mass [7,8], the kilogram, and of temperature [9,10], the Kelvin, will utilize and rely on practical electric quantum standards, realizing the vision of Maxwell [11] and Planck [12] of a truly universal system of units. Both electrical quantum standards require temperatures of 4 K or lower for their operation, but since in addition the QHE only works in a magnetic field, it is practically impossible to combine both in one system. However, in ferromagnetic topological insulators like e.g. Cr-or V-doped (Bi,Sb)2Te3, the quantum anomalous Hall effect (QAHE) provides conductance quantization without a magnetic field [13][14][15][16], giving legitimate hope for a future quantum standard where all units based on ℎ and can be realized in one measurement setup.Yet, up to now the precision of the QAHE has not been tested with precision metrology methods, and in particular no uncertainty budgets were presented with the data published [17,18]. Indeed, the fact that very low measurement currents are required makes it difficult to reach uncertainties in the parts in 10 9 range as are routinely obtained in calibrations based on GaAs or graphene QHE devices. A main reason for the limitation of current is the robustness of the ferromagnetic state, which at this stage of development still requires temperatures in the mK-regime and does not tolerate current levels
An interlaboratory comparison of small-current generation and measurement capability is presented with the ultrastable low-noise current amplifier (ULCA) acting as travelling standard. Various measurements at direct currents between 0.16 nA and 13 nA were performed to verify the degree of agreement between the three national metrology institutes involved in the study. Consistency well within one part per million (ppm) was found. Due to harsh environmental conditions during shipment, the ULCA's transfer accuracy had been limited to about ±0.4 ppm. Supplemental measurements performed at PTB indicate that further improvements in accuracy are possible. Relative uncertainties of 0.1 ppm are achieved by applying on-site calibration of the ULCA with a suitable cryogenic current comparator.
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