Optical Ground Station Proposal for Croatian Quantum Communication Infrastructure

The development of quantum computers, which could potentially implement Shor’s algorithm and thereby pose a threat to classical encryption, has created the need for establishing ultra-secure communication systems. One solution is quantum key distribution (QKD), a method based on the principles of quantum mechanics that enables sharing an encryption key in a way that is fundamentally resilient to computational attacks, quantum or classical. QKD used together with a one-time-pad symmetric cryptography algorithm thus provides information-theoretically secure communication. In addition, QKD enables the detection of any eavesdropping attempt on communications lines. While classical optical communication systems allow signal amplification, the no-cloning theorem from the foundations of quantum mechanics prohibits the cloning of unknown states. This nogo theorem results in the practical limitation of quantum key distribution via optical fibers, prompting the need for free-space solutions. In this work, we present the proposed design of the first Optical Ground Station connected to the terrestrial Croatian Quantum Communication Infrastructure through a QKD node. The station’s function involves receiving prepare-and-measure photons from the low Earth orbit satellite and quantum key generation through the decoy-state BB84 protocol. By utilizing the satellite as a trusted node, this process ensures ultra-secure communication between two optical ground stations.