Introducing Joint Research Project «Quantum Ampere» for the realisation of the new SI ampere

Abstract

Abstract.The metrology community lately has adopted the long-term aim of basing the SI unit system on fundamental constants of nature. The base electrical unit, the ampere, will then be re-defined in terms of a fixed value of the elementary charge e. The most direct realization of the new ampere definition requires 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. State of the art nanofabrication technology allows the fabrication of single-electron transport devices -known as single-electron pumps -which generate electric current by moving electrons one at a time. These devices are capable of delivering currents of about 100 pA with an accuracy at the 1 part per million level. Also, ultrasensitive single-electron detectors have been explored that allow electric charge detection on a resolution level below e. The European Joint Research Project presented here, undertaken by a consortium of several research institutes, aims at further developing the best existing concepts of single-electron pumps and to combine them with single-electron detectors for creating highly accurate quantum current sources, to be used as future current standards. Furthermore, necessary current measurement instrumentation will be developed. The paper comprises the project aims and the main results achieved so far.

Traceable precision generation and measurement of pA direct currents

“…Up to now, only one rather complicated setup was reported that achieved 1 µA/A accuracy [1]. To improve this situation, PTB is pursuing the development of a new picoammeter: the "Ultrastable Lownoise Current Amplifier" (ULCA) is a fully non-cryogenic single-box instrument based on specially designed op-amps and resistor networks, working as current-to-voltage converter [10], [11]. For the experiments reported here, a first prototype with an effective transresistance A tr = U out / I in of 50 MΩ with a temperature coefficient of 1.8 µΩ/Ω per Kelvin was used.…”