透過超穎共振結構設計糾纏量子光源

Abstract

隨著科技的發展，量子相關應用包含量子運算、量子通訊與量子感測等相關應用已逐漸成形。而糾纏量子光源作為驅動上述應用的核心基礎，扮演不可或缺的角色。然而，目前量子光源的體積與尺度仍相對龐大，限制後續的微型化整合與實際應用。若僅對光源進行等比例縮小，其糾纏光子之強度也會大幅縮小到難以滿足使用需求。因此，本研究提出以超穎表面結合非線性晶體之架構，藉由增強局域電場，來提高自發性參數下轉換的效率並提升糾纏光子對產生率。 本研究設計之超穎表面乃基於共振光柵波導的原理，在鈮酸鋰薄膜中形成共振波導模態，以顯著放大局部電場強度。此研究也探討了縮小非線性交互作用之距離下，對非線性效應以及相位匹配條件的影響。此研究採用量子–古典對應分析並使用數值模擬，以計算出糾纏光子之生成效率與空間分布。模擬之結果顯示，超穎表面相較於未加結構之鈮酸鋰薄膜，可大幅提升糾纏光子的生成效率，為後續量子光源微型化與相關應用提供新的可能性。 此外，本研究亦透過硼酸鋇晶體產生並使用單光子偵測器量測糾纏光子對，來探討實際實驗架構對量測光子對結果的影響。實驗之結果除了驗證了糾纏光子的存在、計算整體系統的偵測效率，也分析了準直誤差對實驗結果之影響，為未來量測超穎表面奠定基礎。

With the rapid development of quantum technology, quantum-related applications—including quantum computing, quantum communication, and quantum sensing—have begun to take shape. Entangled-photon sources serve as a fundamental driving element for these applications and therefore play an indispensable role. However, current quantum light sources remain relatively bulky in size, posing challenges for device miniaturization, system-level integration, and practical deployment. Simply scaling down the device dimensions leads to a significant reduction in the brightness of entangled photon pairs, making them difficult to use in realistic scenarios. To address this limitation, this work proposes an integrated architecture that combines a metasurface with a nonlinear crystal to enhance the local electromagnetic field, thereby improving the efficiency of spontaneous parametric down-conversion and increasing the generation rate of entangled photon pairs. The metasurface designed in this study is based on the principle of a resonant waveguide gratings, which excites resonant waveguide modes in a thin-film lithium niobate platform and significantly enhances the local electric field. In addition, we investigate the effects of reducing the nonlinear interaction length on both the nonlinear response and phase-matching conditions. The proposed metasurface design is analyzed using quantum–classical correspondence theory and numerical simulations to evaluate the generation efficiency and spatial modes of entangled photon pairs. Simulation results demonstrate that, compared with an unpatterned lithium-niobate thin film, the metasurface structure can substantially enhance the generation efficiency of entangled photons, offering new possibilities for the miniaturization of quantum light sources and their associated applications. Furthermore, this work experimentally generates and characterizes photon pairs using a β-barium borate crystal together with single-photon detectors, in order to examine how practical measurement configurations affect the characterization of entangled photons. The experimental results not only verify the generation of entangled photon pairs and estimate the overall system detection efficiency, but also analyze the impact of collimation errors on the measurements. These findings establish a foundation for future characterization of metasurface-based quantum sources.