A telecom-wavelength frequency down-conversion based on a cold Rubidium atomic ensemble

Long-distance quantum communication is limited by exponential photon transmission losses in fiber. Typical transitions from ground-level based on neutral atom or iron are in visible wavelengths or near-infrared wavelengths, outside the telecom-wavelength window. Telecom-wavelength conversion is essential to solve this limitation. Here we report our progress in telecom-wavelength frequency down-conversion between 795nm and 1530nm in a cold optically thick gas of Rubidium-87. Based on an EDMOT (Extended Dark Magneto-Optical Trap) with optical density above 30, an efficient four-wave mixing wavelength-conversion is realized. This conversion is using a 5S1/2-5P1/2-4D3/2-5P3/2 diamond configuration, achieving efficiencies up to 16{\%}.