To ensure worldwide consistency and uniformity of measurements, the metrology community lately has adopted the long-term aim of basing the unit system on the fundamental constants of nature. Within this newly proposed SI system the base electrical unit, the ampere, will be re-defined in terms of a fixed value of the elementary charge e.

Electric current is a flow of electrons, which are identical elementary particles each carrying the same charge -e. To realise the new ampere definition requires ways of controlling the number of electrons which flow in a unit time interval, and of counting the errors occurring in this process of clocking single electrons. Thanks to new physical insights combined with advances in nanofabrication technology, it is now possible to build single-electron transport (SET) devices - known as SET pumps - which generate electric current by moving electrons one at a time in a controllable way at sufficiently high speed and accuracy: state-of-the-art SET pumps are capable of delivering currents of about 100 pA with an accuracy at the 1 part-per-million level. Also, ultrasensitive single-electron detectors, based on nanofabricated electrical circuits, have been explored that allow electric charge detection on a resolution level below e.

The project aims at further developing the best existing concepts of SET pumps and to combine them with single-electron detectors for creating highly accurate quantum current sources, to be used as current standards in the future. Furthermore, the necessary associated instrumentation will be developed. The main goals of the three technical work packages are the following:

1. To develop and refine SET pump devices using different anofabrication technologies.

2. To develop the instrumentation necessary for measuring and amplifying single-electron currents and for comparing these current with other reference standards.

3. To test the fundamental quantum accuracy of SET pumps by counting errors at the single electron level, and to develop and implement correction strategies for mitigating errors.

The final result of the project will be a system for realising electric current based on the controlled transfer of electrons. The accuracy of the system will be 0.1 part-per-million or better, and the current will be of the order of 1 μA.

The projected key impact of this JRP is of a fundamental nature, aiming at creating the practical means and methodologies necessary for the realization and dissemination of a new SI base unit definition. In particular the realization of a quantum-based ampere is considered to enable a huge leap in electrical metrology since it overcomes deficiencies inherent in the present SI definition of the ampere, which is based on classical physical effects.

• Within the first six months of its lifetime, the project has successfully developed several kinds of SET pump devices beyond state of the art, being based on metallic (normal and superconducting) and semiconductor systems. Some of these devices already include the single-electron detectors for monitoring charge transport at the quantum level. First SET pump current accuracy measurements with single electron detectors have been demonstrated, and the present work status is well on target with the project aims regarding electrical current level and detection accuracy. Furthermore, new high precision current measurement instrumentation is being developed, being based on cryogenic current comparator systems. These instruments will be suited for measuring a 100 pA quantum generated current at the 0.1 ppm accuracy level.

The outcomes of the project will be disseminated among the stakeholders, which are the relevant bodies of the international metrology and science community, also beyond Europe.

The project runtime is May 01, 2012 – April 30, 2015.

Further details about the project are shown here.

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