The transmittance fluctuation resulting from free space optics will impart the continuous-variable quantum key distribution (CV-QKD). In this paper, we study the CV-QKD over free space by taking practical transmittance fluctuation into account. The transmittance is modeled following the Gaussian distribution, which reflects the most realistic fluctuation since all sources of perturbation are required to be incorporated together in practice. The comprehensive comparison between the practical model and existing models in secret key rate is drawn. The numerical results reveal that the existing model of uniform distribution underestimates the impact of air link for both slow and fast fading scenarios, and the practical secret key rate will suffer severer degradation. Further, as the variance of the Gaussian model decreases, the secret key rate degrades as well. Also, a comparison between heterodyne and homodyne detection schemes is made, and we found that the heterodyne detection outperforms the homodyne detection in the secret key rate for both the slow and fast fading air quantum channels.

中文翻译：

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具有实用链接的自由空间连续变量量子密钥分配

由自由空间光学器件引起的透射率波动将赋予连续可变的量子密钥分布（CV-QKD）。在本文中，我们通过考虑实际的透射率波动来研究自由空间上的CV-QKD。透射率是按照高斯分布建模的，它反映了最现实的波动，因为在实践中需要将所有扰动源合并在一起。对实用模型与现有模型的秘密密钥率进行了全面比较。数值结果表明，现有的均匀分布模型低估了空中链路对慢速和快速衰落情况的影响，实际的秘密密钥率将遭受更大的恶化。此外，随着高斯模型的方差减小，秘密密钥率也会降低。此外，在外差和零差检测方案之间进行了比较，我们发现，对于慢速和快速衰落的空气量子通道，外差检测在秘密密钥率方面均优于零差检测。