QKD arrangement
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.
1. A QKD (quantum key distribution) arrangement comprising:
a photon source for generating pairs of entangled idler photons and signal photons during use, wherein the photon source is adapted for a pulsed delivery of the pairs of photons;
two measuring units, the idler photons being fed to one of the two measuring units and the signal photons being fed to the other one of the two measuring units during use, each of the two measuring units comprising:
an optical module having several photon channels, a photon passing only one of the photon channels as a function of its polarization during use, wherein photon delay units with different pre-fixed delaying periods are comprised in the photon channels in the optical module; and
a detection device for detecting such a photon in association with its respective photon channel, wherein each detection device being one single photon detector and the respective passed-through photon being associated to its respective photon channel on the basis of a time pattern;
a first interrupting unit upstream of the other measuring unit for pulse-wise supplying the signal photons to the optical module during use; and
a time controller which adjusts the detection devices of the two measuring units with a view to the correlated detection of the photons of each such pair.
2. The QKD arrangement of claim 1 , wherein one of the photon channels lacks the photon delay unit.
3. The QKD arrangement of claim 1 , wherein the photon source comprises a pulsed laser.
4. The QKD arrangement of claim 1 , further comprising a pump laser and an SPDC (spontaneous parametric down conversion) crystal, and a second optical interrupting unit provided for the photon source and arranged in a beam path between the pump laser and the SPDC crystal.
5. The QKD arrangement of claim 4 , wherein the second optical interrupting unit is formed by a mechanical chopper.
6. The QKD arrangement of claim 1 , wherein the first interrupting unit is formed by a mechanical chopper.
7. The QKD arrangement of claim 4 , wherein the second, optical interrupting unit is formed by an electrooptical modulator.
8. The QKD arrangement of claim 1 , wherein the first interrupting unit is formed by an electrooptical modulator.
9. The QKD arrangement of claim 1 , wherein each single photon detector is formed by a single photodiode.
10. The QKD arrangement of claim 1 , wherein each optical module includes a non-polarizing beam splitter and two polarizing beam splitters, the two polarizing beam splitters being arranged in two beam paths downstream of the non-polarizing beam splitter, a λ/2 platelet being interposed in only one of the two beam paths, the two polarizing beam splitters each having two outputs thereby defining four photon channels.
11. The QKD arrangement of claim 1 , wherein the photon delay units are formed by delaying optical guides.
12. The QKD arrangement of claim 1 , wherein each of the photon channels is connected with its associated single photon detector via an optical coupler unit.
13. The QKD arrangement of claim 1 , wherein the time controller includes a synchronization unit.
14. The QKD arrangement of claim 13 , wherein the time controller comprises clock signal units, and wherein the single photon detector of the one measuring unit and the photon source are connected to a first one of the clock signal units, and the single photon detector of the other measuring unit and the first interrupting unit are connected to a second one of the clock signal units, both clock signal units in turn being connected to the synchronization unit.
15. The QKD arrangement of claim 13 , wherein the synchronization unit is configured with a phase-locked loop.