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In the development of photonic quantum networks [1], a crucial role will be played by the sources of entangled and single photons. Among the different possible candidates for this role, semiconductor quantum dots [2] are one of the most promising: They can emit single and entangle photons with on-demand operation, with intrinsically low multi-photon probability [3], high indistinguishability [4], and high degree of entanglement [4]. Recent developments in the engineering of these sources produced a device which combines the high extraction efficiencies of photonic cavities with state-of-the-art strain tuning techniques to erase fine structure splitting from potentially any quantum dot and reach at the same time a high brightness and a high entanglement degree of the pair of emitted photons [5]. Using this device as a single source of entangled photon pairs, we were able to demonstrate a proof-of-concept experiment in which two photons, which were previously not correlated, are entangled via entanglement swapping and then used to perform an entanglement-based quantum key distribution [6]. The results show that by a suitable temporal filter of the interfering photons in the entanglement swapping is possible to successfully distribute a quantum key between two parties with the intrinsic security ensured by the laws of quantum mechanics. This protocol, performed with a single source of entangled photons simulating two distant sources, sets a first step towards the practical realization of real-life quantum networks in which entanglement is shared between distant nodes via entanglement swapping and then exploited to perform quantum communication protocols such as quantum key distribution.
[1] C.-Y. Lu, J.-W. Pan, Nat. Nanotechnol. 16, 1294–1296 (2021)
[2] P. Lodahl, Quantum Sci. Technol. 3, 013001 (2018)
[3] L. Schweickert et al., Appl. Phys. Lett. 112, 093106 (2018)
[4] D. Huber et al., Nat. Commun. 8, 15506 (2017)
[5] Rota, M.B., Krieger, T.M., Buchinger, Q. et al. eLight 4, 13 (2024).
[6] Rota, M.B., et al. In preparation (2024)
