The two-qubit controlled-NOT gate is one of the central entangling operations in quantum information technology. The controlled-NOT gate for single photon qubits is normally realized as a network of five individual beamsplitters on six optical modes. Quantum walks (QWs) are an alternative photonic architecture involving arrays of coupled waveguides, which have been successful for investigating condensed matter physics, however, have not yet been applied to quantum logical operations. Here, we engineer the tight-binding Hamiltonian of an array of lithium niobate-on-insulator waveguides to experimentally demonstrate the two-qubit controlled-NOT gate in a QW. We measure the two-qubit transfer matrix with 0.938 ± 0.003 fidelity, and we use the gate to generate entangled qubits with 0.945 ± 0.002 fidelity by preparing the control photon in a superposition state. Our results highlight a new application for QWs that use a compact multi-mode interaction region to realize large multi-component quantum circuits.

中文翻译：

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绝缘体上铌酸锂光子量子行走中的量子逻辑控制非门


二量子位控制的非门是量子信息技术中的核心纠缠运算之一。单光子量子位的受控非门通常实现为六种光学模式上的五个独立分束器的网络。量子行走（QW）是一种涉及耦合波导阵列的替代光子架构，它已成功用于研究凝聚态物理，但尚未应用于量子逻辑运算。在这里，我们设计了绝缘体上铌酸锂波导阵列的紧束缚哈密顿量，以实验演示 QW 中的两个量子位受控非门。我们以 0.938±0.003 保真度测量双量子位传输矩阵，并通过在叠加态准备控制光子，使用门生成保真度为 0.945±0.002 的纠缠量子位。我们的结果突出了量子阱的一种新应用，即使用紧凑的多模相互作用区域来实现大型多组件量子电路。