Single-photon detector in the microwave range

Single-photon counting at microwave frequencies around 500 GHz is demonstrated by using a single-electron transistor (SET) formed by two capacitively coupled ${\mathrm{GaAs/Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{As}$ parallel quantum dots (QDs). A point contact separating the double QDs allows the prompt escape of an excited electron from one of the QDs to another. The resulting long-lived photoinduced ionization of the QD is detected as a change in the SET current.