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 Ba-138(+) ions. Entanglement between the Zeeman sublevels of the ground state of a single Ba-138(+) ion and the polarization state of a single 493 nm photon emitted by the ion with a fidelity of 0.84 +/- 0.01 was achieved, along with a Bell signal of 2.3, exceeding the classical limit of 2 by more than eight standard deviations. This system is a promising candidate for a loophole-free Bell inequality violation test using long-range ion-ion entanglement as the wavelengths of the transitions of Ba-138(+) are in the visible region and thus suitable for long-range transmission over fiber optic cable. (C) 2014 Optical Society of America