Quantum key distribution provides secure keys with information-theoretic security ensured by the principle of quantum mechanics. The continuous-variable version of quantum key distribution using coherent states offers the advantages of its compatibility with telecom industry, e.g., using commercial laser and homodyne detector, is now going through a booming period. In this review article, we describe the principle of continuous-variable quantum key distribution system; focus on protocols based on coherent states, whose systems are gradually moving from proof-of-principle lab demonstrations to in-field implementations and technological prototypes. We start by reviewing the theoretical protocols and the current security status of these protocols. Then, we discuss the system structure, the key module, and the mainstream system implementations. The advanced progresses for future applications are discussed, including the digital techniques, system on chip, and point-to-multipoint system. Finally, we discuss the practical security of the system and conclude with promising perspectives in this research field.

中文翻译：

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连续变量量子密钥分配系统：过去、现在和未来

量子密钥分发提供了由量子力学原理保证的具有信息论安全性的安全密钥。使用相干态的量子密钥分配的连续变量版本具有与电信行业兼容的优点，例如使用商用激光器和零差探测器，目前正处于蓬勃发展时期。在这篇综述文章中，我们描述了连续变量量子密钥分配系统的原理；重点关注基于相干态的协议，其系统正逐渐从原理验证实验室演示转向现场实施和技术原型。我们首先回顾理论协议和这些协议当前的安全状态。然后，我们讨论了系统的结构、关键模块以及主流的系统实现。讨论了未来应用的先进进展，包括数字技术、片上系统和点对多点系统。最后，我们讨论了系统的实际安全性，并总结了该研究领域的前景。