- 學位論文
用於量子光儲存之寬頻單光子源
Broadband Single-Photon Source for Quantum Light Storage
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摘要
在量子通訊及計算的領域中，量子記憶體可用於儲存或是讀取用於傳輸資料的光子，並扮演著不可或缺的角色。由於不同量子電腦之間均由光子進行資料傳輸，不論是應對長距離量子通訊所發展的量子中繼站，抑或是終端的資料寫入，均需要量子記憶體完成這些工作。 基於原子系統的寬頻量子記憶體，因應不同的物理架構共有三種協議。在此其中，基於超輻射現象的記憶體協議最能有效滿足需求。然而，當光子波長接近共振躍遷波長，頻率寬度及原子密度越來越大時，色散導致的波包變形及吸收率會顯著改變甚至降低，影響儲存品質及效率。基於此，讀取時可透過反向讀取的技術以減少失真。然而，我們發現傳統的正向讀取技術雖會導致波包的變形，其程度是與光學深度有相當程度的關係。因此，雖然我們並不會特別使用正向讀取來取出波包，卻可以透過此方式來確認系統的光學深度。 另一方面，糾纏光子對的物理特性無論是對於傳輸的資訊安全，或是實驗上的方便性，都是一個相當誘人的光源系統。它的不可複製性，及遠端操控調製的特性，都使其成為量子通訊領域中主流的研究對象。其中，以自發下參量轉換機制生成的糾纏光子對更是以相對簡單的架設，高重複率，及輕量化的優勢獲得眾多研究的青睞。在本篇論文中，我們使用自發下參量轉換得到的光子對，研究原子系統對於寬頻脈衝的吸收狀況。
並列摘要
In quantum communication and quantum computing, a quantum memory (QM) plays a critical role in storing or reading photons used to share information. These message-encoded photons are called the flying qubits. Since communications between two quantum computers or receivers are accomplished via photons, there is great potential for quantum memories to participate in terminals or quantum repeaters. There are three protocols for atom-based broadband quantum memories, differentiated by distinct physical regimes. Comparing the three protocols, superradiance (SR) memory can achieve higher efficiency with lower optical depth (OD) requirements. However, as a photon passes through the whole medium, the waveform would be distorted due to anomalous dispersion, leading to high infidelity. The technique of backward retrieval is developed to suppress waveform distortion. Nevertheless, we find that the traditional setup of forward retrieval allows the system OD to be provided by the oscillation period of the output field. Entangle photon pairs, or heralded single-photons, are attractive photon sources, valued for experimental convenience and information security. Their unique properties, including non-cloning characteristics and the capability of non-local modulation, make them a major research topic. Comparing the heralded single-photon sources, spontaneous parametric down-conversion (SPDC) particularly attracts researchers due to its relatively simple, compact setup, and high repetition rate. In this thesis, we use entangled photon pairs generated via SPDC to investigate the absorption of an atomic 2-level system.
參考文獻
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