The absence of the single-photon nonlinearity has been a major roadblock in developing quantum photonic circuits at optical frequencies. In this paper, we demonstrate a periodically poled thin film lithium niobate microring resonator (PPLNMR) that reaches 5,000,000%/W second-harmonic conversion efficiency—almost 20-fold enhancement over the state-of-the-art—by accessing its largest ${\chi ^{(2)}}$ tensor component ${d_{33}}$ via quasi-phase matching. The corresponding single-photon coupling rate $g\!/\!2\pi$ is estimated to be 1.2 MHz, which is an important milestone as it approaches the dissipation rate $\kappa\! /\!2\pi$ of best-available lithium niobate microresonators developed in the community. Using a figure of merit defined as $g/\kappa$, our device reaches a single-photon nonlinear anharmonicity approaching 1%. We show that, by further scaling of the device, it is possible to improve the single-photon anharmonicity to a regime where photon blockade effect can be manifested.

中文翻译：

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周期性极化的铌酸锂微环谐振器的单光子非谐性达到1％

缺少单光子非线性已经成为开发光频率量子光子电路的主要障碍。在本文中，我们演示了一种周期性极化的薄膜铌酸锂微环谐振器（PPLNMR），通过获得最大的$ 2，它可以达到5,000,000％/ W的二次谐波转换效率，几乎是最新技术的20倍。{\ chi ^ {（2）}} $张量分量$ {d_ {33}} $通过准相位匹配。相应的单光子耦合率$ g！/ \！2 \ pi $估计为1.2 MHz，这是一个重要的里程碑，因为它接近耗散率$ \ kappa !！/ \！2 \ pi $社区中开发出的最实用的铌酸锂微谐振器。使用定义为$ g / \ kappa $的品质因数，我们的设备达到了接近1％的单光子非线性非谐波。我们表明，通过进一步缩放该设备，可以将单光子非谐性提高到可以显示光子阻挡效应的状态。