The present invention introduces a detector that is able to detect single microwave photons propagating in a waveguide. The waveguide of the invention is lowered to a temperature where it becomes superconductive. Disposed between a middle wire and a ground plane of the waveguide is a very small piece of a desired normal metal, whereby so-called SN contacts are formed between these materials. A separate reflection measurement circuit is coupled to the normal metal piece. When the impedance of the waveguide is matched to the impedance of the normal metal piece as well as possible, a photon propagating in the waveguide is most likely absorbed in the normal metal. The absorption slightly raises the temperature of the piece, which further changes the impedance observed in a so-called SIN junction between the reflection measurement circuit and the piece. The changed amplitude and phase are detectable at the outlet obtained from a mixer of the reflection measurement circuit, whereby a single absorbed photon can be detected. In principle, the present method and device enable quantum calculation in view of future applications.
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