A charge parity ammeter

A metallic double-dot is measured with radio frequency reflectometry. Changes in the total electron number of the double-dot are determined via single electron tunnelling contributions to the complex electrical impedance. Electron counting experiments are performed by moni-toring the impedance, demonstrating operation of a single electron ammeter without the need for external charge detection. Single electron ammeters count each individual electron that passes. They enable the detec-tion of tiny (I < aA) currents;1 show the real-time dynamics of single electron tunnelling;2,3 and may be of use in metrology for the definition of the Ampere.4–8 These devices are made possible by high sensitivity, high bandwidth charge detection which can register the passage of an elec-tron through multiple island single electron devices.9 Typically the charge detector employed is the single electron transistor10 or quantum point contact,11–13 which may be operated in a radio-frequency impedance matching circuit to increase both bandwidth and sensitivity.14–16 In this Let-ter we show that use of external electrometry is unnecessary, simplifying the fabrication of a single electron ammeter. Rather, the internal tunnelling processes within a metallic double dot can be used to herald the passage of single electrons through the system, so the double dot acts as its own ∗To whom correspondence should be addressed 1 a