A high-rate source for single photons in a pure quantum state
  We report on the efficient generation of single photons, making use of spontaneous Raman scattering in a single trapped ion. The photons are collected through in-vacuum high-NA objectives. Photon frequency, polarization and temporal shape are controlled through appropriate laser parameters, allowing for photons in a pure quantum state. 
Christoph Kurz, Jan Huwer, Michael Schug, Philipp M\"uller, and   J\"urgen Eschner
quant-ph