Frequency-locked turnstile device for single electrons

We have fabricated an array of ultrasmall tunnel junctions which acts like a turnstile for single electrons. When alternating voltage of frequency f is applied to a gate, one electron is transferred per cycle through the device. This results in a current plateau in the current-voltage characteristic at I=ef. The overall behavior of the device is well explained by the theory of Coulomb blockade of electron tunneling. We discuss the accuracy limitations of this device.