CROSSING Research Seminar: Entangled Photon Pair Sources for Multi-User QKD – Towards a TU Darmstadt-wide Quantum Key Network

11.02.2021 13:00-14:00

Speaker: Erik Fitzke, TU Darmstadt | Location: Online (Networking afterwards)

Organizer: Johannes Braun, CROSSING

Quantum key distribution (QKD) enables the exchange of symmetric cryptographic keys based on quantum states. Fundamental laws of quantum information theory guarantee that every eavesdropper inevitably changes the statistics of the quantum-physical measurements when trying to obtain information about the shared key. From a statistical analysis of the measurement outcomes, bounds for the leaked information can be derived. This allows countermeasures like privacy amplification. It is provable that afterwards the eavesdropper will not have any information about the final key. Until now, the field of QKD research mainly focused on two-party key exchange. Instead, in project P4 we work on a multi-user QKD system enabling parallel, independent, pairwise key distribution in a star-shaped network.

The source of quantum-mechanically entangled photon pairs is key to the multi-user system. In this talk, recent results of a two-party system developed in P4 will be discussed. The extension to 4 and 2N parties will be outlined. Features of the new, robust, compact source design currently employed in a field-trial under real-world conditions at the Deutsche Telekom facility will be presented along with performance parameters of the 2-party system. The modular design of the source makes the source easily extendable. The realization of the upgrade for 4-party operation will be shown.

Although compact and robust, the current source design must be further integrated in order to make widespread application of QKD feasible. Integrated photonic chips as a possible step towards highly-integrated photon pairs sources for our multi-party QKD system will be considered. Together with recent improvements in our receiver design, this paves the way towards a city-wide QKD network in Darmstadt in CROSSING phase III. Our plans for such a network will be discussed with respect to possible inter-project collaborations in CROSSING regarding a Transfer Project with Deutsche Telekom.

Short Bio
Erik is a PhD student in the Laser and Quantum Optics group led by CROSSING-PI Prof. Thomas Walther.