Room-temperature single-photon source with near-millisecond built-in memory

Non-classical photon sources are a crucial resource for distributed quantum networks. Photons generated from matter systems with memory capability are particularly promising, as they can be integrated into a network where each source is used on-demand. Among all kinds of solid state and atomic quantum memories, room-temperature atomic vapours are especially attractive due to their robustness and potential scalability. To-date room-temperature photon sources have been limited either in their memory time or the purity of the photonic state. Here we demonstrate a single-photon source based on room-temperature memory. Following heralded loading of the memory, a single photon is retrieved from it after a variable storage time. The single-photon character of the retrieved field is validated by the strong suppression of the two-photon component with antibunching as low as $g^{(2)}_{\text{RR|W=1}} = 0.20 \pm 0.07$. Non-classical correlations between the heralding and the retrieved photons are maintained for up to $\tau_{\text{NC}}^{\mathcal R} = (0.68\pm 0.08)$ ms, more than two orders of magnitude longer than previously demonstrated with other room-temperature systems. Correlations sufficient for violating Bell inequalities exist for up to $\tau_{\text{BI}} = (0.15 \pm 0.03)$ ms.