本論文研究了有限長度脈衝光打入 EIT 介質後的損耗程度。根據不同模態的光
互相獨立的性質，利用傅立葉轉換將打入的探測光脈衝轉換至頻域得到各個模態的
分布函數，我們建立了一個多模態的模型並計算出一個平均的量子保真度來量化
EIT 介質保護探測光脈衝的能力。利用這個理論模型我們也比較了佛克態與同調態
在不同光學深度下改變探測光的脈衝長度對穿透率與保真度的影響，並解釋這兩種
量子態各自的量子特性造成了在量子保真度上的差異，包括佛克態的隨機相位以及
同調態中真空態成分的貢獻。

We construct a model to analyze the fidelities for the multimode light fields passing through an electromagnetically-induced-transparency system. Using the Maxwell-Schrödinger and Heisenberg-Langevin equations, we analyze the evolution of the quantum state of the field, and obtain the output density matrix which allows us to calculated the fidelity. The results show that for the Fock-state field, the fidelity depends mainly on transmission. On the contrary, if the input field is coherent state, the fidelity depends on transmission and phase.

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