A device capable of counting the individual electrons in an electric current, by feeding them through a pair of quantum dots, has been developed by scientists in Japan. The device can spot the "backscattering" that occurs when electrons travel the wrong way through a circuit. Previous work in Sweden could not thje direction of the current.
Toshima Fujisawa and colleagues at NTT Basic Research Laboratories in Atsugi, Japan, created a circuit incorporating a two quantum dots - semiconducting crystals just a few nanometres in diameter - which only let a single electron pass through at a time.
After switching the current on, they used another nanoscale device, called a quantum point contact, to measure the charge contained within each quantum dot.