Single-electron current sources: Toward a refined definition of the ampere

TLDR

Control of electrons at the elementary charge was demonstrated in the 1980s, and since then generating a current ef at a drive frequency f has been a metrological focus. The review aims to discuss the generic physical phenomena and technical constraints that influence single‑electron charge transport. It surveys a broad variety of proposed realizations of single‑electron current sources and discusses key issues of readout and potential error‑correction schemes. Several proposed single‑electron current sources have experimentally approached the stringent accuracy and speed required for quantum metrology, while others remain speculative but potentially competitive if technical constraints are overcome; the review also outlines their status within the broader context of electric quantum standards, the future SI system, and non‑metrological applications.

Abstract

The control of electrons at the level of the elementary charge $e$ was demonstrated experimentally already in the 1980s. Ever since, the production of an electrical current $ef$, or its integer multiple, at a drive frequency $f$ has been a focus of research for metrological purposes. This review discusses the generic physical phenomena and technical constraints that influence single-electron charge transport and presents a 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. The important issues of readout of single-electron events and potential error correction schemes based on them are also discussed. Finally, an account is given 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 applications and uses of single-electron devices outside the metrological context are briefly discussed.