SI base

Proposed SI base units using quantum electrical units


The SI ampere will soon be redefined, with the existing definition based on mechanical forces being replaced by a definition based on the quantisation of charge. All electrons have an identical charge, something which can be used to form the basis for the definition of electrical current.

The size of the electron charge is presently measured to be e = 1.602 176 6208(98) × 10−19 Coulombs in the present SI system. Fixing this as a constant in a new system of units enables new ways to produce precise standards of electrical current.



Single electron pumps  can transport electrons one at a time at high speed. Moving individual electrons at a known rate though a circuit using these devices gives a very precise standard of current. Quantum standards of resistance and voltage can also be used to realise quantum electrical units in a manner consistent with the fixing of the quantisation of the electronic charge.


Schematic representation of an electron pump


Practical realisation of an electron pump in a semiconductor device











The Consortium

We are a group of European National Measurement Institutes and other research institutions with expertise in single electron devices, quantum electrical standards and precision measurements of small currents.


We aim to support future primary electrical metrology based on single-electron devices.

Our objectives are to develop:

  • Single-electron-based current sources at a current level of ≈1 nA with uncertainty at, or below, 1 part in 107.
  • Tests of universality, robustness and reproducibility of single-electron-based current sources for the practical realisation of the SI ampere.
  • High-accuracy current measurement capability across NMIs for the testing of various types of single-electron devices.
  • Guidelines for testing the accuracy of single-electron-based current standards.

A key aim is to facilitate the take up of the technology and measurement infrastructure developed by the project by the measurement supply chain (accredited laboratories, instrumentation manufacturers) and end users (industries where small-current measurements at pico-ampere and femto-ampere levels are required).

Formally, the project is divided into four interconnected workpackages.