本論文實驗主要是增加雙光子訊號的訊號背景比。在本論文開始前我們已藉由四波混頻機制在熱原子系統中看到雙光子訊號，然而，雙光子訊號的訊號背景比僅有0.2。我們認為雙光子的背景來自於自發輻射的螢光，其頻率與偏極都與雙光子訊號相同，因此無法用濾偏極元件或是法布里佩羅干涉儀阻絕這些背景螢光。為了降低背景螢光的影響，我們打入一道精細光學幫浦光，將原子分布幫浦至我們期待的能階態，直接減少能參與自發輻射的原子。我們以兩種不同的方式將精細光學幫浦光加入我們的系統中。其一為高斯光斑的精細光學幫浦光加時序，此條件下，我們將雙光子訊號背景比提升至1.25；其二為甜甜圈狀光班的精細光學幫浦光，此條件下，我們將雙光子訊號背景比提升為1.3。

The purpose of our experiment is to enhance the biphoton signal-to-background ratio. In the work prior to the content of this thesis, we have already observed the signal of biphotons, i.e., pairs of single photons with opposite polarizations and wavelengths of 780 nm and 795 nm using a hot atomic vapor cell. However, the fluorescence background created by spontaneous emissions of the atoms in the vapor cell has the same frequency as the biphoton signal’s so that our etalon filter cannot block this fluorescence. As a result, the signal-to-background ratio at the beginning of this work was only 0.2. In order to reduce the background level, we apply another hyperfine optical pumping beam to pump atoms to the desired state. Two different ways to employ the hyperfine optical pumping are used, including the Gaussian beam hyperfine optical pumping with time sequence and the hollow-shaped beam hyperfine optical pumping. After applying the hyperfine optical pumping using either way, we successfully enhance the biphoton signal-to-background ratio to 1.25 or 1.3, respectively.

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