A joint innovation by the National Physical Laboratory (NPL) and the University of Cambridge could pave the way for the Ampere to be redefined in terms of fundamental physical constants.
The Ampere – one of the seven base units of the SI system – is defined officially in terms of the force generated between two parallel wires placed 1m apart in a vacuum. However, this is seen as not being sufficiently accurate. The NPL's solution is a graphene single electron pump (SEP), which provides the speed of electron flow needed to create a new standard for electrical current based on electron charge. An SEP creates a flow of individual electrons by shuttling them into a quantum dot and emitting them one at a time at a well defined rate. A good SEP, says NPL, pumps one electron at a time to ensure accuracy, but pumps them quickly to generate a sufficiently large current. While SEPs made of aluminium are very accurate, they pump electrons too slowly. Graphene's semi metallic 2d structure has the properties needed to let electrons on and off the quantum dot at gigahertz frequencies. Malcolm Connolly, an NPL research associate from the University of Cambridge, said: "We have work to do before we can use this research to redefine the ampere, but this is a major step towards that goal. We have shown that graphene outperforms other materials."