The construction of photon-photon quantum phase gate based on photonic nonlinearity has long been a fundamental issue, which is vital for deterministic and scalable photonic quantum information processing. It requires not only strong nonlinear interaction at the single-photon level, but also suppressed phase noise and spectral entanglement for high gate fidelity. In this paper, we propose that high-quality factor microcavity with strong ${\chi }^{(2)}$ nonlinearity can be quantized to anharmonic energy levels and be effectively treated as an artificial atom. Such artificial atom has a size much larger than the photon wavelength, which enables passive and active ultra-strong coupling to traveling photons. High-fidelity quantum control-phase gate is realized by mediating the phase between photons with an intermediate artificial atom in a photonic molecule structure. The scheme avoids the two-photon emission and thus eliminates the spectral entanglement and quantum phase noises. Experimental realization of the artificial atom can be envisioned on the integrated photonic chip and holds great potential for single-emitter-free, room-temperature quantum information processing.

中文翻译：

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具有χ（2）非线性的光子分子中的光子-光子量子相门

长期以来，基于光子非线性的光子-光子量子相门的构建一直是一个基本问题，这对于确定性和可扩展的光子量子信息处理至关重要。它不仅需要单光子级的强非线性交互作用，而且还需要抑制相位噪声和频谱纠缠以实现高栅极保真度。在本文中，我们建议使用高质量的微腔${\chi }^{（2）}$非线性可以量化为非谐波能级，并可以有效地视为人造原子。这样的人造原子的尺寸远大于光子波长，这使得能够与行进的光子进行被动和主动的超强耦合。通过将光子之间的相与光子分子结构中的中间人工原子介导，可以实现高保真量子控制相门。该方案避免了双光子发射，从而消除了光谱纠缠和量子相位噪声。可以在集成光子芯片上设想人造原子的实验实现，并且在无单发射体的室温量子信息处理中具有巨大的潜力。