Fast Photon-Mediated Entanglement of Continuously Cooled Trapped Ions for Quantum Networking

We entangle two cotrapped atomic barium ion qubits by collecting single visible photons from each ion through in vacuo 0. 8 NA objectives, interfering them through an integrated fiber beam splitter and detecting them in coincidence. This projects the qubits into an entangled Bell state with an observed fidelity lower bound of F>94%. We also introduce an ytterbium ion for sympathetic cooling to remove the need for recooling interruptions and achieve a continuous entanglement rate of 250 s^-1.