Manipulating Electrons One by One

Abstract

We describe three circuits based on nanoscale tunnel junctions with which we manipulate single electrons. Their operating principle is based on “macroscopic charge quantization”: at low temperature, the charges in the metallic islands between the junctions correspond to integer numbers of electrons and their fluctuations are quenched due to the electrostatic energy gap arising from the small value of the island capacitances. The simplest circuit we have operated is the “single electron box”: one junction and one capacitor define a single island which we have charged with one electron at a time. To monitor the entrance of one extra electron on the island we have used a single electron transistor, which consists of two nanojunctions in series, as a very sensitive electrometer. We have designed and operated two other devices, the pump (3 junctions) and the turnstile (4 junctions), through which electrons are transferred one by one by means of gate voltages capacitively coupled to the islands. When this controlled transfer of electrons is clocked at a frequency /, both devices produce a d.c. current I = ef.