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中国物理学会期刊

基于超纠缠的三用户全连接量子网络

CSTR: 32037.14.aps.74.20250458

A three-user fully connected quantum network based on hyperentanglement

CSTR: 32037.14.aps.74.20250458
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  • 超纠缠作为一种多自由度上的高维量子纠缠现象, 在量子通信、量子计算和高维量子态操控中发挥着关键作用. 与单一自由度纠缠态不同, 超纠缠态在偏振、路径、轨道角动量等多个自由度上同时建立纠缠关系, 通过纠缠操控分发技术, 可以构建出高维量子信息网络. 基于此, 本文构建了一个超纠缠的全连接量子网络, 通过周期极化薄膜铌酸锂(PPLN)波导级联二次谐波产生和自发参量下转换过程实现偏振和time-bin自由度的超纠缠, 并使用密集波分复用(DWDM)技术, 将超纠缠态复用到单模光纤中传输给终端用户. 使用Franson-type干涉和双光子符合测量技术对纠缠态的质量进行表征, 同时对偏振纠缠态进行了量子态层析, 并利用纠缠分发技术在网络中实现长距离分发及量子密钥传输. 实验结果表明, 偏振纠缠和time-bin纠缠的双光子干涉对比度均大于95%, 并且在经过100 km纠缠分发后, 两种自由度的量子态保真度依旧高于88%, 证明了该网络具有高质量的超纠缠, 并且可以实现远距离的纠缠分发. 本文的方法为构建支持量子隐形传态、超密集编码等量子任务的大规模超纠缠的量子网络提供了一种新的方案.

     

    Hyperentanglement, as a high-dimensional quantum entanglement phenomenon with multiple degrees of freedom, plays a critical role in quantum communication, quantum computing, and high-dimensional quantum state manipulation. Unlike entangled states in a single degree of freedom, hyperentangled states establish entanglement relationships simultaneously in multiple degrees of freedom, such as polarization, path, and orbital angular momentum. Through entanglement-based distribution techniques, high-dimensional quantum information networks can be constructed. On this basis, a fully connected quantum network with hyperentanglement is constructed in this work, and the polarization and time-bin degree-of-freedom hyperentanglement is realized through the process of second-harmonic generation and spontaneous parametric down-conversion in periodically poled lithium niobate (PPLN) waveguide cascades. The hyperentangled state is then multiplexed into a single-mode fiber by using dense wavelength division multiplexing (DWDM) technology for transmission to terminal users. The quality of the entangled states in the two degrees of freedom is characterized using Franson-type interference and photon-pair coincidence measurement techniques. Polarization entangled states are subjected to quantum state tomography, and entanglement distribution technology is employed to achieve long-distance distribution and quantum key transmission within the network. Experimental results show that the two-photon interference visibility of both polarization and time-bin entanglement is greater than 95%, demonstrating the high quality of the hyperentanglement in the network. After 100-km-entanglement distribution, the fidelity of the quantum states in both degrees of freedom remains above 88%, indicating the effectiveness of long-distance entanglement distribution in this network. Additionally, it is verified that this network supports the distribution of quantum keys over a distance of more than 50 km between users. These results confirm the feasibility of a fully connected quantum network with hyperentanglement and demonstrate the potential for constructing large-scale metropolitan networks by using hyperentanglement. As a higher-dimensional entanglement, hyperentangled states can significantly enhance the capacity and efficiency of quantum information processing. Although the quantum communication is still in its early stages of development, achieving stable storage and transmission of entangled states in large-scale metropolitan networks remains a great challenge. By utilizing the frequency conversion properties and high integration characteristics of the periodically poled lithium niobate waveguides, the three-user hyperentangled quantum network constructed in this work provides a new solution for developing the large-scale metropolitan networks with high-dimensional quantum information networks. It is expected to provide a new platform for quantum tasks such as superdense coding and quantum teleportation.

     

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