论文标题
明亮的纠缠光子源没有严格的晶体温度和激光频率稳定
Bright entangled photon source without stringent crystal temperature and laser frequency stabilization
论文作者
论文摘要
纠缠的光子源（EPS）是各种量子通信协议的主要构件，通常是通过在$χ^{2} $非线性散装光学材料中利用自发参数下转换（SPDC）开发的。虽然高非线性和长相互作用长度已经确定了EPS的定期螺旋晶体的优势，但此类晶体的相匹配条件对晶体温度和激光波长的波动非常敏感。结果，将这些来源部署在实验室外面，例如基于卫星的应用程序，要求严格的质量和电力预算，从而提高任务的复杂性和成本。我们报告了一个明亮，稳定的纠缠光子源，其晶体温度和激光波长稳定的需求松弛。使用周期性的SAGNAC干涉仪内的定期螺栓固定的KTP晶体，在环形环中以810 nm的形式在810 nm的环形环中产生变性的，型0相匹配的光子对，我们将SPDC环转换为一个“完美”环，借助两个常见的光学元素，Axicon和镜头。尽管SPDC环的大小从高斯向不同直径的环形变化，因为晶体温度在$ 7^{o} $ C上的变化变化，而激光波长超过300 GHz，我们观察到“完美”环的大小是恒定的。新的EPS具有高达22.58 $ \ pm $ 0.15 kHz/mw的光谱亮度，该单模光纤带有铃铛参数，s = 2.64 $ \ pm $ 0.05，量子状态保真度为0.95 $ \ pm $ 0.02，以前需要$ 0.8^$ $ 0.8^$ 0.8^$} $ 0.8^$} EPS。该通用方案可用于所有晶体中的非电线SPDC光子，以在任何波长和时间尺度上开发用于资源受限应用的时间尺度。
Entangled photon sources (EPS), the major building block for a variety of quantum communication protocols, are commonly developed by utilizing the spontaneous parametric down-conversion (SPDC) in $χ^{2}$ nonlinear bulk optical materials. While high nonlinearity and long interaction length have established the superiority of the periodically poled crystals for EPSs, the phase-matching condition of such crystals is very sensitive to the fluctuation of the crystal temperature and the laser wavelength. As a result, deploying such sources outside the laboratory, for example, satellite-based applications, demands a stringent mass and power budget, thus enhancing the mission complexity and cost. We report a bright, stable entangled photon source with a relaxed requirement of crystal temperature and laser wavelength stabilization. Using a periodically poled KTP crystal inside a polarization Sagnac interferometer producing degenerate, type-0 phase-matched entangled photon pairs at 810 nm in an annular ring, we have transformed the SPDC ring into a "perfect" ring with the help of two common optical elements, axicon, and lens. Despite the variation of the SPDC ring size from Gaussian to annular of different diameters due to the change of crystal temperature over $7^{o}$C, and laser wavelength over 300 GHz, we observe the size of the "perfect" ring to be constant. The new EPS, having a spectral brightness as high as 22.58 $\pm$ 0.15 kHz/mW collected using single-mode fiber with a Bell's parameter, S = 2.64 $\pm$ 0.05, and quantum state fidelity of 0.95 $\pm$ 0.02, requires a crystal temperature stability of $\pm$ $0.8^{o}$C, almost five times relaxation as compared to the previous EPS. The generic scheme can be used for non-collinear SPDC photons in all crystals to develop EPS at any wavelength and timescales for resource-constrained applications.
