A coherent transmission methodology for a continuous-variable quantum key distribution (CV-QKD) system based on quantum-heterodyne measurement through a coherent intradyne receiver is experimentally demonstrated in the framework of 5G mobile fronthaul links. Continuous optical carrier synchronization is obtained through training information, which is multiplexing to the quantum signal as pilot tone in both, frequency and polarization. Spectral tailoring by means of optical carrier suppression and single-sideband modulation is adopted to simultaneously mitigate crosstalk into the quantum channel and self-interference for the pilot tone, thus allowing for a high signal-to-noise ratio for this training signal. Frequency offset correction and optical phase estimation for the free-running local oscillator of the receiver is accurately performed and guarantees low-noise quantum signal reception at high symbol rates of 250 MHz and 500 MHz with additional Nyquist pulse shaping. A low excess noise in the order of 0.1% to 0.5% of shot-noise units is obtained for fiber-based transmission over a fronthaul link reach of 13.2 km. Moreover, co-existence with 11 carrier-grade classical signals is experimentally investigated. Joint signal transmission in the C-band of both, quantum signal and classical signals, is successfully demonstrated. Secure-key rates of 18 and 10 Mb/s are obtained under strict security assumptions, where Eve has control of the receiver noise, for a dark and a lit fiber link, respectively. Moreover, rates of 85 and 72 Mb/s are resulting for a trusted receiver scenario. These secure-key rates are well addressing the requirements for time-shared CV-QKD system in densified 5G radio access networks with cloud-based processing.

中文翻译：

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用于密集 5G 无线电网络的高速 CV-QKD 安全移动 WDM 前传

在 5G 移动前传链路的框架中，通过相干内差接收器基于量子外差测量的连续可变量子密钥分配 (CV-QKD) 系统的相干传输方法进行了实验证明。连续的光载波同步是通过训练信息获得的，该信息在频率和偏振上作为导频复用到量子信号中。采用通过光载波抑制和单边带调制的频谱调整，以同时缓解进入量子信道的串扰和导频音的自干扰，从而为该训练信号提供高信噪比。接收器的自激本地振荡器的频偏校正和光相位估计得到准确执行，并通过额外的奈奎斯特脉冲整形确保在 250 MHz 和 500 MHz 的高符号率下接收低噪声量子信号。对于前传链路范围 13.2 公里上的基于光纤的传输，获得了大约 0.1% 到 0.5% 散粒噪声单位的低过量噪声。此外，实验研究了与 11 个载波级经典信号的共存。成功证明了量子信号和经典信号在 C 波段的联合信号传输。18 和 10 Mb/s 的安全密钥速率是在严格的安全假设下获得的，其中 Eve 可以控制接收器噪声，分别适用于暗光纤链路和亮光纤链路。而且，85 Mb/s 和 72 Mb/s 的速率产生于可信接收器场景。这些安全密钥速率很好地满足了具有基于云处理的密集 5G 无线电接入网络中的分时 CV-QKD 系统的要求。