Ion-Photon Entanglement and Bell Inequality Violation with 138Ba+

We report on the demonstration of ion-photon entanglement and Bell inequality violation in a system of trapped 138Ba+ ions. Entanglement between the Zeeman sublevels of the ground state of a single 138Ba+ ion and the polarization state of a single 493 nm photon emitted by the ion with a fidelity of $0.84\pm0.01$ was achieved, along with a Bell signal of 2.3, exceeding the classical limit of 2 by over eight standard deviations. This system is a promising candidate for a loophole-free Bell inequality violation test as the wavelengths of the transitions of 138Ba+ are in the visible region and thus suitable for long range transmission over fiber optic cable.