Single-electron Counting Device (Single-electron Ammeter)
A single-electron counting device for detecting individual electron flow in an electric current has been developed. Quantum dots (L and R in the figure) and a point contact electrometer are integrated in a compound semiconductor device, which allows us to measure the location of an electron passing through the quantum dots. The current through the point contact shows three-level fluctuations as shown in the right panel, from which each electron motion (tunneling event) is identified. The device works as an ultimate current meter with single-electron sensitivity. (Page 32)