Scheme for generating a sequence of single photons of alternating   polarisation
  Single-photons of well-defined polarisation that are deterministically generated in a single spatio-temporal field mode are the key to the creation of multi-partite entangled states in photonic networks. Here, we present a novel scheme to produce such photons from a single atom in an optical cavity, by means of vacuum-stimulated Raman transitions between the Zeeman substates of a single hyperfine state. Upon each transition, a photon is emitted into the cavity, with a polarisation that depends on the direction of the Raman process. 
T. Wilk, H. P. Specht, S. C. Webster, G. Rempe, and A. Kuhn