通訊波段多光子糾纏光源是實現量子通訊與分散式量子資訊處理的重要資源，其中四光子糾纏態可作為擴展光子量子網路的平台。然而，在以自發參數下轉換產生糾纏光子對並透過光子融合生成四光子糾纏態的過程中，多光子對事件會不可避免地伴隨理想單光子對事件產生，進而形成非理想的符合計數，降低干涉對比度與四光子態保真度。為了分析此限制，本論文建立一個多光子噪音模型，用以描述自發參數下轉換的高階項對糾纏光源的影響，並將平均每脈衝光子對數、偵測效率等實驗參數納入模型中，以預測四光子態在不同雷射功率下的保真度。在實驗架構上，本研究使用基於偏振糾纏薩格納克干涉儀的第二型自發參數下轉換光源製造兩對高保真糾纏光子對，並使用偏振分光器將來自兩對干涉儀的光子干涉用以形成四光子糾纏。此外，本研究量測不同雷射功率下的平均每脈衝光子對數，並確認其與雷射功率近似呈線性關係。理論預測顯示，隨著雷射功率增加，多光子噪音會使對比度與四光子態保真度下降；相反地，在低功率下，多光子噪音可被有效抑制，使預測之保真度下界可成功超越0.8536的理論邊界值，該值定義了具純正四體非局域性之量子關聯可被古典模型模擬的極限。進一步地，本論文將準光子數解析偵測器(pseudo-photon-number-resolving detector)的噪音剔除機制(discarding)納入模型中，結果顯示此機制可提升預測的對比度與保真度下界。本論文建立之多光子噪音模型與分析方法，可作為評估與優化高保真度通訊波段四光子糾纏光源的理論基礎。

Telecommunication-wavelength multipartite entangled photon sources are essential resources for implementing quantum communication and distributed quantum information processing, among which the four-photon entangled state serves as a pivotal platform for scaling up photonic quantum networks. However, during the process of generating entangled photon pairs via spontaneous parametric down-conversion (SPDC) and subsequently generating four-photon entangled states through photon fusion, multi-pair photon emission events inevitably accompany the single-pair generations. This results in non-ideal coincidence counts, which degrade both the interference visibility and the four-photon state fidelity. To analyze this physical limitation, we establish a multi-photon noise model to characterize the impacts of higher-order SPDC terms on the entanglement source. Crucial experimental parameters, such as the mean pair number per pulse and detection efficiencies, are incorporated into the framework to predict the state fidelity under various laser powers. In terms of the experimental architecture, we utilize type-II SPDC sources configured within polarization Sagnac interferometers (PSIs) to produce two pairs of high-fidelity entangled photons. A polarizing beam splitter (PBS) is then employed to interfere the photons from the two independent interferometers, successfully forming the four-photon entanglement platform. Additionally, the mean pair number per pulse across different laser power levels is experimentally measured, confirming an approximately linear relationship with the pumping power. Theoretical predictions indicate that as the laser power increases, multi-photon noise leads to a significant decline in visibility and four-photon state fidelity. Conversely, in the low-power regime, the multi-photon noise can be effectively suppressed, allowing the predicted fidelity lower bound to successfully surpass the theoretical threshold of 0.8536, which defines the limit of classically simulable correlations from genuine four-partite nonlocality. Furthermore, this thesis incorporates the noise discarding mechanism of pseudo-photon-number-resolving (pseudo-PNR) detectors into the model. The results demonstrate that this mechanism can substantially enhance both the predicted visibility and the fidelity lower bound. The developed multi-photon noise model and analytical methodology establish a robust theoretical foundation for evaluating and optimizing high-fidelity telecommunication-wavelength four-photon entanglement sources.

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