We demonstrate atom-photon entanglement using a single cesium atom trapped in an optical tweezer. Entanglement is generated by resonant excitation and subsequent spontaneous decay, which entangles the atomic Zeeman state with photon polarization. The emitted photon is coupled into a single-mode fiber, enabling measurement of the Bell-state fidelity. We obtain raw entanglement fidelity of $\mathcal{F}=0.942(16)$ and inferred fidelity of ${\mathcal{F}}_{\inf }=0.962(26)$ after correcting independently characterized atom measurement errors. Compared with related free-space experiments using ${}^{87}\mathrm{Rb}$, the Zeeman substructure of the relevant excited level in ${}^{133}\mathrm{Cs}$ requires the use of a single short excitation pulse in each entanglement attempt in order to suppress unwanted re-excitation. These results establish a free-space ${}^{133}\mathrm{Cs}$ atom-photon interface and provide a step toward dual-species Rb-Cs quantum networking.

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• Entanglement production
• Quantum communication
• Quantum communication, protocols & technology
• Trade networks