Recent work on high-dimensional photonic entanglement in Optica Quantum. This study demonstrates the generation of an entangled state in the time-energy domain, encoded in the photon-number basis, using a solid-state three-level quantum system. By employing energy- and time-resolved correlation experiments in combination with extensive theoretical modeling, we characterized the entanglement structure of the generated state and determined an upper bound for its fidelity to the entangled target state, yielding F ≤ 70%. Building upon previous studies, which demonstrated time-entanglement in photon-number encoding from two-level quantum systems [S.C. Wein et al., Nature Photonics 16, 374–379 (2022)], our work extends these findings to three-level systems. Recent theoretical research [A. C. Santos et al., Opt. Lett. 48, 6332 (2023)] has suggested that sequential resonant excitation of such systems could generate high-dimensional entanglement. Our experimental implementation involved a semiconductor quantum dot system comprising biexciton, exciton, and ground states. The quantum dot samples, based on droplet-etched GaAs/AlGaAs structures, were grown by Armando Rastelli and Saimon Filipe Covre da Silva. Entanglement is a key resource in quantum information science, and our results contribute to advancing its applications. The photonic entanglement generated in this study has potential use in quantum communication protocols and high-density information encoding. Notably, previous research has shown that this form of entanglement can achieve a mutual information exceeding that of a Greenberger–Horne–Zeilinger (GHZ) state [A. C. Santos et al., Opt. Lett. 48, 6332 (2023)]. This research was made possible through a collaboration between: Technische Universität Berlin: Daniel Vajner, Nils D. Kewitz, and Martin von Helversen Universidad Autónoma de Madrid: Carlos Antón Solanas Quandela: Stephen Wein Johannes Kepler Universität Linz: Armando Rastelli Universität Innsbruck: Saimon Filipe Covre da Silva, Yusuf Karlı, Vikas Remesh, Florian Kappe, and Gregor Weihs. [Full article]
