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Defining electrical units of measurement in terms of universal constants allows precise standards to be established. Both the unit of volt and ohm can be defined from the elementary charge e and the Planck constant by exploiting the Josephson effect and the quantum Hall effect, respectively.

However, an equivalent, robust standard for the ampere is still lacking. One proposal is to use single-electron pumps i.e. quantum devices that shuffle electrons one at a time with a certain frequency f , so that the standard of current can be defined from the product of the elementary charge and the frequency (ef).The drawback is that these devices operate in the tunnelling regime, whose stochastic nature results in fluctuations of the measured current from the value ef.

Scientists at the Physikalisch-Technische Bundesanstalt Institute have now experimentally demonstrated a device configuration that can overcome this problem. They have implemented a series of three single-electron pumps and two charge detectors, which monitor the flow of electrons across the pumps. Single electrons are shuffled across by applying voltage pulses to each pump in a certain sequence. Then, subsequent pulses allow the detection of pumping errors, that is, of events in which a pump fails to shuffle an electron. The knowledge of these errors allows, in turn, the current fluctuations to be determined from ef, and eventually to achieve a tenfold improvement in accuracy compared with the case of individual electron pumps.

Single Electron Source

Figure: SEM image of the device. The semiconductor part between source and drain (green) consists of three pumps and two charge nodes (blue, red). Each pump is
defined by three metallic top gates (yellow) forming a QD in the semiconductor.

 

Article @ DOI: 10.1103/PhysRevLett.112.226803

Edited and Extracted from Reliable single-electron source by Elisa De Ranieri

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