基于光学量子行走, 设计了一个能够实现远程光子偏振态和空间态交换的方案, 使得光子的低质量偏振纠缠与高质量空间纠缠发生互换, 最终使远程通信双方获得最大偏振纠缠态。也就是说, 利用光子在空间自由度上的远程纠缠资源来辅助, 可提高光子在偏振自由度上的远程纠缠。所有的后选择结果都是成功的, 因此这里的态交换是确定性的。该方案不仅适用于Werner态, 还适用于任意未知的远程光子偏振态, 因此该方案还具有普适性。方案中的半波片和光束移位器都是成熟的光学器件, 所以该方案简单易行, 为远程偏振纠缠操控提供了另一种备选方案。

Experimental engineering of high-dimensional quantum states is a crucial task for several quantum information protocols. However, a high degree of precision in the characterization of the noisy experimental apparatus is required to apply existing quantum-state engineering protocols. This is often lacking in practical scenarios, affecting the quality of the engineered states. We implement, experimentally, an automated adaptive optimization protocol to engineer photonic orbital angular momentum (OAM) states. The protocol, given a target output state, performs an online estimation of the quality of the currently produced states, relying on output measurement statistics, and determines how to tune the experimental parameters to optimize the state generation. To achieve this, the algorithm does not need to be imbued with a description of the generation apparatus itself. Rather, it operates in a fully black-box scenario, making the scheme applicable in a wide variety of circumstances. The handles controlled by the algorithm are the rotation angles of a series of waveplates and can be used to probabilistically generate arbitrary four-dimensional OAM states. We showcase our scheme on different target states both in classical and quantum regimes and prove its robustness to external perturbations on the control parameters. This approach represents a powerful tool for automated optimizations of noisy experimental tasks for quantum information protocols and technologies.

Quantum walks, a counterpart of classical random walks, have many applications due to their neoteric features. Since they were first proposed, quantum walks have been explored in many fields theoretically and have also been demonstrated experimentally in various physical systems. In this paper, we review the experimental realizations of discrete-time quantum walks in photonic systems with different physical structures, such as bulk optics and time-multiplexed framework. Then, some typical applications using quantum walks are introduced. Finally, the advantages and disadvantages of these physical systems are discussed.