Photon antibunching in resonance fluorescence - the emission from a single, resonantly driven two-level quantum emitter - is a paradigmatic signature of nonclassical light. Photon entanglement, by contrast, manifests as correlations that can defy any classical description and is typically regarded as a distinct quantum effect. Here, we experimentally extract pairs of narrowband, time-bin-entangled photons from the antibunched resonance fluorescence of a single trapped atom. We verify entanglement via violation of the CHSH Bell inequality and by reconstructing the two-photon density matrix. The observed correlations vanish when the coincidence time window exceeds the antibunching timescale, revealing underlying multimode entanglement in the emitted field. Our results establish a direct link between photon antibunching and photon-photon entanglement, unifying two canonical signatures of nonclassical light.
@article{arxiv.2504.11294,
title = {On the Relationship Between Antibunching and Entanglement in Resonance Fluorescence},
author = {Xin-Xin Hu and Gabriele Maron and Luke Masters and Arno Rauschenbeutel and Jürgen Volz},
journal= {arXiv preprint arXiv:2504.11294},
year = {2026}
}