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THU: Thursday Contributed Sessions
THU 13: Poster Session: Applications
THU 13.11: Poster
Thursday, September 11, 2025, 16:30–18:30, ZHG Foyer 1. OG
Characterization and mitigation of optical side-channels in QKD — •Evelyn Edel1, Moritz Birkhold1,2, Sebastian Mahlik4, Harald Weinfurter1,2,3, and Lukas Knips1,2,3 — 1Ludwig Maximilian University, Munich, Germany — 2Munich Center for Quantum Science and Technology, Munich, Germany — 3Max Planck Institute of Quantum Optics, Garching, Germany — 4University of Gdańsk, Gdańsk, Poland
Unlike classical key distribution methods reliant on computationally hard problems, quantum key distribution (QKD) achieves information-theoretic security by the principles of quantum physics. The decoy-state BB84 protocol offers a practical scheme for realizing free-space QKD sender modules, allowing the use of highly attenuated laser pulses as a photon source. However, imperfections in devices could enable side-channel attacks by an eavesdropper.
This work presents a characterization of spectral side-channels in our sender module. To prepare the different polarization states, four vertical-cavity surface-emitting lasers (VCSELs) in a monolithic array are used, which results in imperfect spectral overlap opening up a side-channel. The spectral behavior of over 100 VCSELs was characterized under varying bias and modulation currents. Together with the time-resolved pulse analysis enabled by a streak camera, this allows identification of arrays with optimal spectral overlap and facilitates future module optimization. First steps were taken to quantify the information leakage via mutual information, which will be used to appropriately adjust privacy amplification in the protocol.
Keywords: QKD; Quantum Key Distribution; BB84; Satellite-based Quantum Communication