Quantum Key Distribution in Real-World Metropolitan Network SettingsHYBRID

With the advent of quantum computers, many widely used cryptographic algorithms such as RSA will be rendered insecure. Quantum key distribution (QKD) can pave the way to a secure infrastructure, providing the secure distribution of symmetric keys to enable further encryption of valuable data across metropolitan networks. The main advantage of QKD in contrast to other approaches is that unconditional security of a key exchange can be guaranteed based on the laws of quantum mechanics without assuming a certain computational power of an attacker.

There are various implementations of QKD protocols either for aerial or fiber link-based transmission relying on photons to transmit the data. Most key exchange setups involve only two parties, or focus solely on the experiment and concepts without considering constraints introduced by the post-processing of the keys. However, experimental setups are prone to errors which must be accounted for. Especially, field trials of QKD systems come with additional challenges impacting the performance of the systems.

We are presenting the first experiments of our star-shaped QKD network consisting of several pairs of parties being able to exchange keys simultaneously, thus supporting up to 100 parties [1]. The experiment has been conducted with a field deployed fiber, demonstrating the robustness of our protocol. In contrast to other experiments, we do not rely on the polarization of exchanged photons, thus drastically simplifying our setup, as then there is no need to monitor the transmission fiber.

Furthermore, to achieve a complete key exchange session we also consider post-processing of the keys. The latter can drastically influence the key generation rate, hence thorough optimization is required. We present how post-processing impacts the key generation and how this can be mitigated. To conclude we outline the importance and challenges of a real field test trial in a city-wide distributed setup.

[1] Fitzke, E., Bialowons, L., Dolejsky, T., Tippmann, M., Nikiforov, O., Walther, T., Wissel, F. & Gunkel, M. (2022). Scalable network for simultaneous pairwise quantum key distribution via entanglement-based time-bin coding. PRX Quantum, 3(2), 020341.

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