Freiburg 2024 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 21: Quantum Communication III

Q 21.3: Talk

Tuesday, March 12, 2024, 11:30–11:45, HS 3219

Phase stabilization for fiber based CV QKD — •Sophie Verclas, Benedict Tohermes, and Roman Schnabel — Institut für Quantenphysik und Zentrum für Optische Quantentechnologien, Universität Hamburg, Deutschland

Quantum Key Distribution (QKD) is a technology for secure communication between two parties, using the principles of quantum mechanics. Our QKD experiment implements a fiber-based, continuous variable QKD scheme, connecting two laboratories in two separated buildings (building A and B). We set up an EPR entanglement source in building A, consisting of two squeeze lasers and overlapped their outputs at a 50/50 beamsplitter to generate two-mode squeezed states, which are shared between the two buildings via optical fiber.

In both buildings, the entangled states are measured with balanced homodyne detectors. Due to the entanglement, the results are random but also correlated and can be used to generate a secret key. Attacks on the channel as well as on devices in building B reduce the entanglement strength and can thus be quantified.

A major challenge in this setup is the phase stabilization and synchronization between the two buildings. In this presentation I will introduce the experiment, discuss the problem of phase noise and our approach to a control scheme for its compensation.

Keywords: Cryptography; Fiber QKD; Entanglement; Squeezed light; Phase stabilization