Generation of frequency multiplexed entangled single photons assisted by   the entanglement
  We present a scheme to generate the frequency multiplexed entangled (FME) single photons based on the entanglement between two species atomic mixture ensemble. The write and reads fields driven according to a certain timing sequence, the generation of FME single photons can be repeated until success is achieved. The source might have significant applications in wavelength division multiplexing quantum key distribution. 
Chun-Hua Yuan, L. Q. Chen, Z. Y. Ou, Weiping Zhang
quant-ph