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Q: Fachverband Quantenoptik und Photonik

Q 20: QuanTour II – Multi-photon Effects & Entanglement

Q 20.4: Talk

Tuesday, March 3, 2026, 12:00–12:15, P 7

Challenges and Advances Toward Maximal Entanglement in Quantum Dot Emitters — •Francesco Basso Basset for the QD-E-QKD photon source collaboration — Department of Physics, Politecnico di Milano, Milan, Italy

Quantum dots have become established sources of highly polarization-entangled photons, aiming to overcome trade-offs between brightness and entanglement. Despite evidence of nearly dephasing-free operation, open questions remain on the practical limits. This talk recaps experiments identifying mechanisms that must be controlled to reach near-unity entanglement, including multipair emission from re-excitation, spin noise from hyperfine interactions, and challenges in cavity-integrated devices operated at high brightness and GHz rates.

First, we report evidence of a recently proposed limitation in the standard on-demand scheme, resonant two-photon excitation of the biexciton-exciton cascade. The effect, linked to the optical Stark shift, strengthens as emission overlaps the excitation pulse, calling for dedicated mitigation. Second, we examine an often overlooked degree of freedom: emission angle. Photon momentum and polarization are correlated, especially in microcavities, introducing which-path information that reduces polarization entanglement. A simple dipole-emission model captures the behavior and guides the design of structures that maximize extraction efficiency without compromising fidelity.

These results show that key aspects of quantum-emitter behavior remain unresolved, and it is still too early to set limits on the future role of this technology in quantum networks.

Keywords: quantum dot; entanglement; nanophotonics; optical microcavities; quantum communication