BOULDER, Colo. Physicists at the National Institute of Standards have found a way to build a device that can reliably count individual electrons. The new approach results from studies of electrons that were confined to Cooper pair boxes at temperatures close to absolute zero. A Cooper pair box confines superconducting electrons inside a box that sandwiches aluminum oxide between two layers of aluminum. The presence of a pair can be detected by highly sensitive measurements of the superconducting current in the box.
Using the method of superconductivity, researchers can count Cooper pairs very precisely. But some electrons in the box remain unpaired.
The researchers discovered that there are variations in the bonds holding the pairs together. After conducting a controlled study of those variations, they realized that they could build a Cooper box that would have fewer unpaired electrons. Previously, the unpaired electrons introduced a random factor that showed up in measurements as noise.
The researchers are now convinced that the noise can be reduced to the point where a Cooper box-based device would be able to count individual electrons. They hope to use their insights into Cooper pairing to develop new fundamental standards for single-electron devices.