In practical quantum communication networks, the scheme of continuous-variable quantum key distribution (CVQKD) faces a challenge that the entangled source is controlled by a malicious eavesdropper, and although it still can generate a positive key rate and security, its performance needs to be improved, especially in secret key rate and maximum transmission distance. In this paper, we proposed a method based on the four-state discrete modulation and a heralded hybrid linear amplifier to enhance the performance of CVQKD where the entangled source originates from malicious eavesdropper. The four-state CVQKD encodes information by nonorthogonal coherent states in phase space. It has better transmission distance than Gaussian modulation counterpart, especially at low signal-to-noise ratio (SNR). Moreover, the hybrid linear amplifier concatenates a deterministic linear amplifier (DLA) and a noiseless linear amplifier (NLA), which can improve the probability of amplification success and reduce the noise penalty caused by the measurement. Furthermore, the hybrid linear amplifier can raise the SNR of CVQKD and tune between two types of performance for high-gain mode and high noise-reduction mode, therefore it can extend the maximal transmission distance while the entangled source is untrusted.

中文翻译：

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通过 Heralded 混合线性放大器改进具有不可信源的离散调制连续可变量子密钥分发的性能

在实际的量子通信网络中，连续可变量子密钥分发（CVQKD）方案面临的挑战是纠缠源被恶意窃听者控制，虽然它仍然可以产生正密钥率和安全性，但其性能需要改进，特别是在密钥速率和最大传输距离方面。在本文中，我们提出了一种基于四态离散调制和预兆混合线性放大器的方法，以提高 CVQKD 的性能，其中纠缠源来自恶意窃听者。四态 CVQKD 通过相空间中的非正交相干态对信息进行编码。它比高斯调制具有更好的传输距离，尤其是在低信噪比 (SNR) 下。而且，混合线性放大器将确定性线性放大器(DLA)和无噪声线性放大器(NLA)串联起来，可以提高放大成功的概率，减少测量带来的噪声损失。此外，混合线性放大器可以提高CVQKD的信噪比，并在高增益模式和高降噪模式两种性能之间进行调谐，因此可以在不信任纠缠源的情况下延长最大传输距离。