正向共振四波混頻在雙Λ架設下，由於無法避免的自發輻射影響，有著轉換效率25%的上限。本論文中證明在使用反向配置雷射的情況下能夠有效的壓抑自發輻射，在反向雙Λ的系統中，在光學密度48的實驗條件下，得到的四波混頻轉換效率可以達到63.3%。根據理論預測，反向四波混頻在光學密度約500時有著接近100%的轉換效率，如此高效率的頻率轉換在全光學量子信號處理中有著潛在的應用性。此外，實驗中成功利用光學幫浦準備集中度95.8% 的單一賽曼態。在高光學密度的條件下，觀察到輻射捕捉效應對於居量集中的破壞。

Resonant four-wave mixing(FWM)based on a double-Λ scheme has a maximum conversion efficiency (CE) of 25% due to unavoidable spontaneous emission. Here, we demonstrate the spontaneous emission can be greatly suppressed by arranging the applied laser beams with a backward configuration. With the backward double-Λ scheme, we observe the FWM efficiency can reach 63.3% in cold rubidium atoms with an optical depth of 48, which is the first observation of the CE exceeding 25% in the resonant
double-Λ FWM system. According to the theoretical predictions, this backward FWM scheme can achieve near 100% CE using a medium with a large optical optical depth
of around 500. Such an efficient frequency conversion scheme may have potential applications in all-optical quantum signal processing. Moreover, we prepare populations in a single-Zeeman state with 95.8% of concentration by using optical pumping. Under
highly concentrated condition, we observe the potential difference between multi-Zeeman states and a single-Zeeman state.

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