Underwater quantum communication has recently been explored using polarization and orbital angular momentum (OAM). Here, we show that spatially structured modes, e.g., a coherent superposition of beams carrying both polarization and OAM, can also be used for underwater quantum cryptography. We also use the polarization degree of freedom to investigate the impact of the channel length on key rates for quantum communication applications. The underwater channel proves to be a difficult environment for establishing quantum communication as underwater optical turbulence results in significant beam wandering and distortions. However, the errors associated to the turbulence do not result in error rates above the threshold for establishing a positive key in a quantum communication link with both the polarization and spatially structured photons. The impact of the underwater channel on the spatially structured modes is also investigated at different distances using polarization tomograph...

中文翻译：

---

使用结构化光子研究30米水槽中的水下量子通道

最近已经使用极化和轨道角动量（OAM）探索了水下量子通信。在这里，我们显示了空间结构化模式，例如同时带有偏振和OAM的光束的相干叠加，也可以用于水下量子密码学。我们还使用极化自由度来研究信道长度对量子通信应用中关键速率的影响。水下通道被证明是建立量子通信的困难环境，因为水下光学湍流会导致明显的光束漂移和畸变。但是，与湍流相关的错误不会导致错误率高于在具有极化和空间结构化光子的量子通信链路中建立正密钥的阈值之上。