Entanglement is a central resource in quantum technologies, and the realization of photonic entanglement necessarily relies on interaction with matter. Resonance fluorescence (RF), originating from the coherent interaction between a driving field and a two-level system, plays a pivotal role in quantum optics. Here, we demonstrate a novel route to entanglement generation based on RF from a single quantum dot. Rather than relying on generation of multiphoton states, our approach directly exploits vacuum-one-photon number superposition states created under resonant excitation. By delocalizing this superposition via a beam splitter, we realize time-bin entanglement and observe a clear violation of the Clauser-Horn-Shimony-Holt Bell inequality using Franson-type interferometry. Our scheme removes the need for multiphoton generation, simplifies the experimental requirements, and establishes a scalable pathway toward solid-state entangled photon sources.
@article{arxiv.2511.15413,
title = {Bell Inequality Violation with Vacuum-One-Photon Number Superposition States},
author = {Zi-Qi Zeng and Jian Wang and Xiu-Bin Liu and Xu-Jie Wang and Li Liu and Hanqing Liu and Haiqiao Ni and Zhichuan Niu and Carlos Antón-Solanas and Bang Wu and Zhiliang Yuan},
journal= {arXiv preprint arXiv:2511.15413},
year = {2025}
}