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Q: Fachverband Quantenoptik und Photonik

Q 49: Quantum Communication, Networks, Repeaters, & QKD I

Q 49.5: Talk

Thursday, March 5, 2026, 12:00–12:15, P 10

What can the experimentalist learn from Bell polytopes? — •Tom Hobbs and Ilja Gerhardt — light & matter group, Institute for Solid State Physics, Leibniz University Hannover, Appelstrasse 2, D-30167 Hannover, Germany

Measurements on entangled systems can produce correlations which are stronger than those predicted by local theories of physics. For a particular experimental configuration, the set of outcomes allowed by local models forms a Bell polytope. Meanwhile, quantum theory allows for a larger outcome set, comprising the whole local polytope plus additional nonlocal correlations. For applications such as quantum key distribution (QKD) or randomness generation, it is important to know whether the measured correlations lie inside or outside the local region. This is typically done by checking if the correlations violate a particular Bell inequality.

In our work we investigate how experimental flaws, such as imperfect state preparation, detector noise, and mismatched measurement bases, affect the set of correlations that can be measured. We show how these correlations can be visualized, and how varying the experimental settings can move the measured correlations inside or outside the Bell polytope. We aim to link our results to a practical entanglement-based QKD scenario.

Keywords: Bell nonlocality; entanglement; quantum key distribution; quantum cryptography; quantum correlations