Analysis of the Public Channel of Quantum Key Distribution Link

Quantum key distribution (QKD) relies on the laws of physics to establish a symmetric binary key between remote parties. A QKD link involves the realization of a quantum channel for the transmission of quantum key material encoded in certain photon properties, as well as a public channel for verification of the exchanged key material. This paper deals with the mutual dependence of these channels and analyzes the impact of performance of both channels on the overall key material establishment process. This paper presents measurement data obtained under laboratory conditions as well as the results obtained by establishing a virtual QKD link. Despite the common beliefs that increased quantum bit error rate implies a larger amount of traffic on the public channel, our measurements prove the opposite. The obtained data clearly show that the public channel has a major impact on the overall performance of the QKD link.