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The ampere: Single-electron tunneling (SET)

One ampere corresponds to the flux of approx. 6 × 1018 electrons per second. By counting the electrons, the ampere can be traced to the second. The precondition for this is that the charge of an electron is exactly known or fixed, as planned in the new SI. For this purpose, single-electron pumps are developed in semiconductor structures in order to realize a precise electrical current by electron counting.

Single-electron pumps in semiconductor structures

Working Group 2.53: Low-dimensional Electron Systems

SET, Current and Charge

Working Group 2.61: SET, Current and Charge



Manipulating individual electrons with the goal of employing quantum effects offers new possibilities and greater precision in electronics. However, these single-electron circuits are governed by the laws of quantum mechanics, meaning that deviations from error-free operation still occur – albeit (in the best possible scenario) only very rarely. Thus, insights into both the physical origin the and...

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In certain magnetic field ranges, fractional (blue curve) and integer QHE lead to resistance values that are only given by the fundamental constants h and e, and by a rational number. The ratio of 1 : 6, which had been predicted theoretically for the two resistance values characterized by the two arrows, has been experimentally confirmed for the first time with a measurement uncertainty of a few parts in 108. The inserted image is a schematic representation of the composite fermion in this fractional QHE regime. The quasi-particle consists of an electron to which two magnetic flux quanta are bound; it carries the charge e/3.

The “new SI”, scheduled for May 2019, is based on fundamental constants which can be directly measured by means of macroscopic quantum effects. Verifying the theoretical fundaments of these effects experimentally with the greatest accuracy is one of the core tasks of metrology. In the case of the quantum Hall effect, this has now been successfully done for the first time for a state in which the...

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SI-Grafik (BIPM)

This revolution has been a long time in the making. Behind it are metrologists working in their scientific laboratories, and scientific managers in their decision-making committees. Now the moment is approaching when many of the old quantities (specifically, the definitions behind them) will have to step down to make way for their successors, who are waiting in the wings. The quantities concerned...

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PTB has topped its own world record established a year ago where electric currents were generated with singleelectron pumps and their quantization was verified with the greatest accuracy by means of a special measuring amplifier. The new record (which was made possible by improving the experimental setup) is a relative measurement uncertainty of only 0.16 μA/A. Moreover, this result was achieved...

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The universe of physics is experiencing great changes: by 2018, scientists want to place all physical base units on solid, unchangeable foundation in the form of fundamental constants. The units "meter" and "second" were well ahead of schedule; now the kelvin, the kilogram, the mole and the ampere are next in line. The research activities of the Physikalisch-Technische Bundesanstalt (PTB) are...

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