  A new approach for realization of a quantum interface between single photons
and single ions in an ion crystal is proposed and analyzed. In our approach the
coupling between a single photon and a single ion is enhanced via the
collective degrees of freedom of the ion crystal. Applications including
single-photon generation, a memory for a quantum repeater, and a deterministic
photon-photon, photon-phonon, or photon-ion entangler are discussed.
