Validation of a quantized-current source with 0.2 ppm uncertainty

Abstract

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.

High-resolution error detection in the capture process of a single-electron pump

“…2(b) and 2(e) we show P N ðV G2L Þ for 0 N 3, obtained from sets of 500 cycles for each V G2L using the slow and fast loading waveforms, respectively. As expected from DC measurements with the pump in a magnetic field, 5,7,8,20 there are a series of wide plateaus where one value of N dominates the loading statistics. This is highlighted by color-coding data points black when all the cycles yielded the same value of N. Comparable data have been presented previously, 9 but at zero magnetic field where the regime of very accurate loading could not be accessed.…”

“…In one example, a dynamically gated QD can pump electrons from a source to a drain electrode, [1][2][3][4] generating an accurate quantized current with metrological application as a new realisation of the ampere. [5][6][7][8] In this application, the accuracy of electron trapping and ejection in the non-adiabatic regime is of key importance. We wish to transfer n electrons in response to a single gate voltage cycle, with an error rate less than 10 À7 .…”

“…The error counting measurements on GaAs pumps 9,10 were performed in zero magnetic field using superconducting single electron transistor (SET) charge detectors, and were therefore not able to access the regime of high accuracy pumping attained in fields >10 T. 5,7,8 Precise single-electron counting tests of semiconductor QD pumps in the high-field, high-accuracy pumping regime are clearly desirable to validate the DC pumping measurements, and also to approach the benchmark error probability of $10 À8 demonstrated for a slow adiabatic metallic pump. 13 In this work, we focus on measuring P N , the probability of loading the QD with N electrons (distinguished from P n , the probability of pumping n electrons).…”

“…The use of a QPC instead of a SET detector 9,10 allows operation in strong magnetic fields. Electrons can be loaded with fast voltage waveforms, as used in high-speed pumping experiments 5,8 and then probed on millisecond time-scales required for high-fidelity readout. We use a 2-stage measurement protocol to suppress the effect of 1/f noise in the QPC due to non-equilibrium charged defects, 18 and we achieve a sufficiently high charge detection fidelity (probability of the charge detection yielding the right answer for N), to probe loading probabilities at the 10 À6 level.…”

“…A magnetic field was applied perpendicular to the plane of the 2-DEG to enhance the current quantization. 5,7,8,20 Our measurement protocol is illustrated by schematic potential diagrams in Fig. 1(c).…”