The ampere is the base unit of electrical current in the International System of units (the SI system).

All electrical and magnetic quantities are influenced by the definition of the ampere.

At present it is formally defined by mechanical forces between wires. This is to be replaced by a more robust definition based on the quantisation of charge

We are developing new ways to create and disseminate precision electrical current standards within this redefined system based on fundamental constants. This includes high speed semiconductor-based single electron pumps, ultra-stable current amplifiers, Josephson and Quantum hall systems for calibrations at intermediate current and capacitor ramp systems at extremely low current levels.

Recent published (open access) scientific results:

 

Knowledge transfer and interaction with end-users

We are working with end-user communities to help them access ultra stable electrical current standards. We are looking for ways in which measurement best practice, the latest instrumentation and information about primary standards can be shared with these users.

Here are some examples of existing interactions with end-users:

If you would like to know how you can interact with the project contact jdf@npl.co.uk.

Background 

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.

SI base

Proposed SI base units using quantum electrical units

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.

pump-electron-movie

Schematic representation of an electron pump

gaaspump

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.

Motivation

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.