Narrowband Polarization-Entangled Photon Source for Quantum Networking with Cesium Atoms

Entanglement distribution based on narrowband photons is an attractive option for emerging quantum networks of atom arrays. Here we describe our experimental approach to demonstrate a cavity-enhanced source of polarization-entangled photons at the Cesium D2 line (852 nm) for quantum networks of atom arrays. The cavity-enhanced spontaneous parametric down-conversion (SPDC) process with a PPKTP crystal can generate narrowband entangled photon pairs tunable to the Cs transition line, enabling entanglement transfer from photons to atoms. This approach eliminates the need for frequency conversion and can achieve versatile optical frequency control for different entanglement schemes. The system can be upgraded to generate entangled photons at different wavelengths, making it a promising tool for connecting distinct atoms in a quantum network.