Jobs & Careers

The novel field of quantum information is promising to revolutionize many aspects of society. Particularly interesting is the possibility of realizing unconditionally secure communications via Quantum Key Distribution: this is a cryptographic primitive that does not rely on any computational assumption, as is standard in present-day cryptography, but whose security is instead guaranteed by the laws of quantum mechanics. A major hurdle to the deployment of QKD is that the intensity of a laser signal decreases exponentially along an optical fiber, limiting the maximum distance at which a optical-fiber QKD link can be established to a few hundreds of kilometers at most. A currently available technological solution to this problem is to use a satellite link instead, exploiting the fact that photons propagate without losses in the space above the atmosphere. The DLR Institute of Communications and Navigation works in the field of optical quantum and classical satellite communications. Currently, the Institute launched a cubesat to test classical communications systems between LEO and ground, the mission called PIXL-1. Future missions shall use the developed laser terminal technology to bring a QKD satellite into orbit.

The aim of the thesis is to characterize the impact of background photons on the quality of the QKD link. In fact, the receiver telescope used for the free-space quantum communication collects photons that are scattered by the satellite and by the atmosphere, resulting in an increased noise in the quantum communication. A preliminary study should investigate which QKD protocols are most resilient to noise and what amount of background photons is to be expected in different scenarios, for instance during daytime or by night. Subsequently, on-the-field measurements of the background photons should be performed and the effectiveness of techniques aiming at rejecting background photons assessed.