Optical fiber links and networks are integral components within and between cities’ communication infrastructures. Implementing quantum cryptographic protocols on either existing or new fiber links will provide information-theoretical security to fiber data transmissions. However, there is a need for ways to increase the channel bandwidth. Using the transverse spatial degree of freedom is one way to transmit more information and increase tolerable error thresholds by extending the common qubit protocols to high-dimensional quantum key distribution (QKD) schemes. Here we use one type of vortex fiber where the transverse spatial modes serves as an additional channel to encode quantum information by structuring the spin and orbital angular momentum of light. In this proof-of-principle experiment, we show that two-dimensional structured photons can be used in such vortex fibers in addition to the common two-dimensional polarization encryption, thereby paving the path to QKD multiplexing schemes.

中文翻译：

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通过涡旋光纤的结构化光子的量子密码学

光纤链路和网络是城市通信基础设施之内和之间不可或缺的组成部分。在现有或新的光纤链路上实施量子密码协议将为光纤数据传输提供信息理论上的安全性。但是，需要增加信道带宽的方法。使用横向空间自由度是一种传输更多信息并通过将通用qubit协议扩展到高维量子密钥分配（QKD）方案来增加可容忍的错误阈值的方法。在这里，我们使用一种涡旋纤维，其中横向空间模式用作通过构造光的自旋和轨道角动量来编码量子信息的附加通道。在这个原理证明实验中，