Opt Express. 2023 Feb 27;31(5):8042-8048. doi: 10.1364/OE.481055.
We experimentally investigate the frequency down-conversion through the four-wave mixing (FWM) process in a cold Rb atomic ensemble, with a diamond-level configuration. An atomic cloud with a high optical depth (OD) of 190 is prepared to achieve a high efficiency frequency conversion. Here, we convert a signal pulse field (795 nm) attenuated to a single-photon level, into a telecom light at 1529.3 nm within near C-band range and the frequency-conversion efficiency can reach up to 32%. We find that the OD is an essential factor affecting conversion efficiency and the efficiency may exceed 32% with an improvement in the OD. Moreover, we note the signal-to-noise ratio of the detected telecom field is higher than 10 while the mean signal count is larger than 0.2. Our work may be combined with quantum memories based on cold Rb ensemble at 795 nm and serve for long-distance quantum networks.
我们通过在具有金刚石能级结构的冷铷原子系综中进行四波混频（FWM）实验，研究了频率下转换过程。通过制备具有 190 的高光学深度（OD）的原子云，实现了高效率的频率转换。在这里，我们将衰减到单光子水平的信号脉冲场（795nm）转换为近 C 波段的 1529.3nm 的电信光，转换效率高达 32%。我们发现 OD 是影响转换效率的关键因素，通过提高 OD，效率可能超过 32%。此外，我们注意到检测到的电信场的信噪比高于 10，而平均信号计数大于 0.2。我们的工作可以与基于 795nm 冷铷原子系综的量子存储器相结合，为远距离量子网络服务。
