基于硬件同步的四态离散调制连续变量量子密钥分发  

Four-state discrete modulation continuous variable quantum key distribution based on hardware synchronization

作　　者：张云杰 王旭阳[1,3] 张瑜[1] 王宁 贾雁翔 史玉琪 卢振国 邹俊[4] 李永民[1,3] Zhang Yun-Jie;Wang Xu-Yang;Zhang Yu;Wang Ning;Jia Yan-Xiang;Shi Yu-Qi;Lu Zhen-Guo;Zou Jun;Li Yong-Min(State Key Laboratory of Quantum Optics and Quantum Optics Devices,Institute of Opto-Electronics,Shanxi University,Taiyuan 030006,China;School of Physics and Electronics Engineering,Shanxi University,Taiyuan 030006,China;Collaborative Innovation Center of Extreme Optics,Shanxi University,Taiyuan 030006,China;ZJU-Hangzhou Global Scientific and Technological Innovation Center,Zhejiang University,Hangzhou 311215,China)

机构地区：[1]山西大学光电研究所,量子光学与光量子器件国家重点实验室,太原030006 [2]山西大学物理电子工程学院,太原030006 [3]山西大学,省部共建极端光学协同创新中心,太原030006 [4]浙江大学,浙江大学杭州国际科创中心,杭州311215

出　　处：《物理学报》2024年第6期128-139,共12页Acta Physica Sinica

基　　金：山西省应用基础研究计划(批准号:202103021224010);山西省省筹资金资助回国留学人员科研项目(批准号:2022-016);国家自然科学基金(批准号:62175138,62205188,11904219);量子光学与光量子器件国家重点实验室开放课题(批准号:KF202006);山西“1331工程”重点项目资助课题。

摘　　要：在连续变量量子密钥分发系统中,同步技术是确保通信双方时钟和数据一致的关键技术.本文通过巧妙设计发送端和接收端仪器的硬件时序,采用时域差拍探测方式和峰值采集技术,实验实现了可硬件同步的四态离散调制连续变量量子密钥分发.通信双方在设计好的硬件同步时序下可实现时钟的恢复和数据的自动对齐,无需借助软件算法实现数据的对齐.本文采用了加拿大滑铁卢大学Norbert Lütkenhaus研究组提出的针对连续变量离散调制协议的安全密钥速率计算方法.该方法需计算出接收端所测各种平移热态的一阶矩和二阶(非中心)矩,以此为约束条件结合凸优化算法可计算出安全密钥速率.计算过程中无需假设信道为线性信道,无需额外噪声的估算.密钥分发系统重复频率为10 MHz,传输距离为25 km,平均安全密钥比特率为24 kbit/s.本文提出的硬件同步方法无需过采样和软件帧同步,减小了系统的复杂度和计算量,在一定程度上降低了系统所需的成本、功耗和体积,有效地增强了连续变量量子密钥分发的实用性.In the case of continuous-variable quantum key distribution(CV-QKD)systems,synchronization is a key technology that ensures that both the transmitter and receiver obtain corresponding data synchronously.By designing an ingenious time sequence for the transmitter and receiver and using the peaking value acquisition technique and time domain heterodyne detection,we experimentally realize a four-state discrete modulation CV-QKD with a repetition rate of 10 MHz,transmitting over a distance of 25 km.With well-designed time sequence of hardware,Alice and Bob can obtain corresponding data automatically without using numerous software calculation methods.The secure key rates are calculated by using the method proposed by the Lütkenhaus group at the University of Waterloo in Canada.In the calculation,we first estimate the first and the second moment by using the measured quadratures of displaced thermal states,followed by calculating the secret key rate by using the convex optimization method through the reconstruction of the moments.There is no need to assume a linear quantum transmission channel to estimate the excess noise.Finally,secure key rates of 0.0022-0.0091 bit/pulse are achieved,and the excess noise is between 0.016 and 0.103.In this study,first,we introduce the prepare-and-measure scheme and the entanglement-based scheme of the four-state discrete modulation protocol.The Wigner images of the four coherent states on Alice’s side,and four displaced thermal states on Bob’s side are presented.Second,the design of hardware synchronization time series is introduced comprehensively.Third,the CV-QKD experiment setup is introduced and the time sequence is verified.Finally,the calculation method of secure key rate using the first and the second moment of quadrature is explained in detail.The phase space distribution of quadratures is also presented.The secret key rate ranges between 0.0022 and 0.0091 bits/pulse,and the equivalent excess noise are between 0.016 and 0.103.The average secret key bit rate is 24 kbit/s.

关 键 词：连续变量量子密钥分发 硬件同步 四态离散调制 时域差拍探测 

分 类 号：O413[理学—理论物理] TN918.4[理学—物理]