Single-electron current sources: towards a refined definition of ampere

TL;DR

This review discusses the development of single-electron current sources for quantum metrology, highlighting physical principles, technological challenges, experimental progress, error correction, and their role in redefining electrical standards and units.

Contribution

It provides a comprehensive overview of various realizations of single-electron sources, evaluating their readiness for metrological applications and discussing future prospects and challenges.

Findings

Some devices nearly meet quantum metrology standards

Error correction schemes are being developed for single-electron transfer

Single-electron devices are integral to future electrical SI units

Abstract

Controlling electrons at the level of elementary charge $e$ has been demonstrated experimentally already in the 1980's. Ever since, producing an electrical current $ef$, or its integer multiple, at a drive frequency $f$ has been in a focus of research for metrological purposes. In this review we first discuss the generic physical phenomena and technical constraints that influence charge transport. We then present the broad variety of proposed realizations. Some of them have already proven experimentally to nearly fulfill the demanding needs, in terms of transfer errors and transfer rate, of quantum metrology of electrical quantities, whereas some others are currently "just" wild ideas, still often potentially competitive if technical constraints can be lifted. We also discuss the important issues of read-out of single-electron events and potential error correction schemes based on them. Finally, we give an account of the status of single-electron current sources in the bigger framework of electric quantum standards and of the future international SI system of units, and briefly discuss the applications and uses of single-electron devices outside the metrological context.