Efficient telecom frequency conversion (TFC) in atomic systems is crucial for integrating atom-based quantum nodes into low-loss fiber-optic quantum networks. Here, we demonstrate high-efficiency TFC from 795 to 1367 nm in a cold ${}^{87}\mathrm{Rb}$ ensemble via diamond-type four-wave mixing (FWM), achieving conversion efficiencies of 66 and 80% at optical depths of 75 and 110, respectively, using a weak coherent probe field. These results surpass all previously reported values in atomic systems, enabled by a systematic investigation of the built-in V-type and cascade-type electromagnetically induced transparency spectra that guided the optimization of FWM conditions. Although this work employs coherent fields, our previous theoretical study has shown that quantum states can be preserved with high fidelity during the conversion process, highlighting the promise of diamond-type atomic FWM as a robust interface for long-distance quantum communication.

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• Cooling & trapping
• Light-matter interaction
• Quantum communication
• Quantum optics
• Atomic ensemble
• Four-wave mixing