A Waveguide Frequency Converter Connecting Rubidium Based Quantum   Memories to the Telecom C-Band
  The ability to coherently convert the frequency and temporal waveform of single and entangled photons will be crucial to interconnect the various elements of future quantum information networks. Of particular importance in this context is the quantum frequency conversion of photons emitted by material systems able to store quantum information, so called quantum memories. There have been significant efforts to implement quantum frequency conversion using non linear crystals, with non classical light from broadband photon pair sources and solid state emitters. However, so far, solid state quantum frequency conversion has not been achieved with long lived optical quantum memories. Here, we demonstrate an ultra low noise solid state photonic quantum interface suitable for connecting quantum memories based on atomic ensembles to the telecommunication fiber network. The interface is based on an integrated waveguide non linear device. As a proof of principle, we convert heralded single photons at 780nm emitted by a rubidium based quantum memory to the telecommunication wavelength of 1552nm. We demonstrate a significant amount of non classical correlations between the converted photon and the heralding signal. 
Boris Albrecht, Pau Farrera, Xavier Fernandez-Gonzalvo, Matteo   Cristiani, Hugues de Riedmatten
quant-ph