在本論文中，我們考慮一個Λ型態的三能階原子系統，具有兩個基態|1〉和|2〉以及一激發態|3〉，利用一道非共振的寫入光脈衝與位於基態|1〉的原子群發生作用，會導致自發拉曼散射機制，並產生頻率小於寫入光且頻率差為兩基態間頻率的史托克光子，同時寫入光脈衝的資訊也記憶於原子群中兩基態間的自旋波。儲存一段時間後，利用一共振於基態|2〉與激發態|3〉的讀取雷射與原子群作用，將原子的同調基態自旋波轉換為頻率為能階|1〉與|3〉共振的反史托克光子釋放出來，此讀取雷射與電磁波引發透明實驗中的耦合雷射扮演相同的角色，使反史托克光子不被處於基態|1〉的原子群吸收，此時史托克光子與反史托克光子具有相關聯性。

本實驗利用暗區自發力光陷阱，捕捉密度極高的冷原子群。在最佳參數條件下，光學密度可達約50，並進行相關的自發拉曼散射實驗。當一頻率為紅調變24 MHz及光強度為 1.1 μW 的寫入雷射與冷原子群作用，研究儲存時間對於取出反托克光子效率的影響。我們觀察到經過 0.33 ms 的儲存時間，取出效率仍有 e-1，說明了光資訊在此時間尺度下可儲存於原子基態的自旋波內。此外，我們研究了在固定儲存時間為 0.15 ms之下，不同寫入光脈衝強度對於取出反托克光子效率的影響。我們發現由於寫入光脈衝內所含的能量不同，所產生的史托克光子能量與反史托克光子能量也隨之變化，證明了史托克光子數與反史托克光子數彼此間具有很強的關聯性。未來利用 原子群製備單光子的實驗中，可以藉由此研究為基礎並加以改善，相信目前的實驗結果對於本實驗室未來實現應用於量子資訊科學上的確定性 ( On-demand single-photon source ) 單光子源與量子儲存記憶體有相當大的幫助。

We consider an atomic ensemble of a three-level “Λ-type” system, with two metastable ground states|1〉and |2〉, and an excited state|3〉. An off-resonant laser, referred to as the “write” laser, is applied to an ensemble that has been optically pumped into the ground state |1〉, resulting in the spontaneous Raman scattering. The step will generate the photons, so called “Stokes photons”, with a frequency less than that of the write laser by an amount equal to the|1〉 and |2〉transition frequency. In this way, the incident photon pulse is mapped onto the atomic coherence ( or referred to “spin wave” ) between|1〉and |2〉. After a storage time, “τ”, a read laser is applied on resonance with the|2〉 - |3〉 transition, converting the atomic coherence into anti-Stokes photons resonant with states|1〉and|3〉. The read laser acts as a coupling laser in the experiment of electromagnetically induced transparency for the anti-Stokes photons, preventing it from being absorbed by the large atomic population in state|1〉.
Our experiment traps cold atomic ensembles with a high optical density of 50 by the dark spontaneous-force optical trap. When the write laser with power is 1.1 μW and red detuning of 24 MHz, interacts with atomic ensembles, we studied the storage-time dependence of the retrieve efficiency of anti-Stokes photons. We observed the storage time of 0.33 ms corresponding to e-1 retrieve efficiency. The spin coherence had a long-lived storage time in metastable ground states| 1〉and | 2〉. In addition, we reported the energy variation of Stokes ( anti-Stokes ) energy in the different write laser powers and pulse widthes and demonstrated the correlation between Stokes and anti-Stokes photons. In the future, we will create an on-demand single-photon source and achieve the quantum memory using atomic ensembles for applications in quantum information science.

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