Switchyard for single electrons

German scientists achieved to transfer very small charge "packets", comprising a well-defined number of few electrons, between metallic electrons precisely by using a single-electron pump. A single-electron transistor, being able to resolve charge variations of a single electron or less, served as a charge detector to monitor the charge movement. The successful experiment is an important milestone on the way to the setup of a new standard for capacitance, where a capacitor is charged by a well-known number of electrons.

The corresponding voltage can be measured using a Josephson voltage standard. Tracing the capacitance to a resistance via the quantum-Hall effect finally allows the realisation of the so-called "Quantum Metrological Triangle", which establishes a link between all three electrical quantum effects. The precision aimed at in the experiment requires the demonstrated manipulation of charge on the scale of a single electron.

Task of this metrology project is the implementation of a new capacitance standard which is based on the quantization of electrical charge in units ofthe elementary charge e.

The basic idea of the experiment is to charge a capacitor with a well-known number of n electrons and to measure the resulting electrical voltage U. Thus, the capacitance C of the capacitor is determined by C = ne / U. Accurate "counting" of the electrons occurs with the help of a special Single-Electron Tunneling (SET) circuit, a so-called SET-pump. If the voltage U is measured by using a Josephson voltage standard (U = ifh / 2e), the capacitance C can be expressed exclusively in terms of the fundamental constants e and h, the frequency f and integer numbers (n and i). Thus, the experiment enables electrical capacitance metrology on quantum basis, as it is already usual for the electrical voltage U (using the Josephson effect) and the electrical resistance R(using the quantum Hall effect).

If the experiment is performed with a relative uncertainty of 10-7 (0.1 ppm), it opens a way to realize the "quantum metrological triangle" which is a consistency test for the three electrical quantum effects involved. The results of this experiment will impact on a future system of units which will be based on fundamental constants.

Source: Physikalisch-Technische Bundesanstalt

Explore further

Boosting the capacity of supercapacitors

Citation: Switchyard for single electrons (2008, February 25) retrieved 27 January 2021 from https://phys.org/news/2008-02-switchyard-electrons.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments