a qkd arrangement with a photon source generating entangled idler and signal photons , with two measuring units , one of which receiving the idler photons and the other one receiving the signal photons , and each including an optical module with photon channels , wherein a photon passes a photon channel as a function of its polarization , and a device for detecting the photons in association to its respective photon channel , as well as a time control for timingly adjusting the detection devices ; the photon source is adapted for pulsed emission of photon pairs , and an interrupting unit supplying the signal photons to the optical module in pulsed manner is arranged upstream of the other measuring unit , the photon channels in each optical module including delay units with different delay periods , and only one single - photon detector associates the photons to the photon channels on the basis of a time pattern .