基于量子中继的星-地量子密钥分发系统安全理论研究

Quantum key distribution (QKD) can provide data security communication between two remote parities over a quantum channel. However, the communication distance is limited to 200 km with current technology due to the signal attenuation. A significant boost in communication speed and distance can only be achieved with quantum relay stations. Therefore, on the way to implement the information security transmission of satellite-ground QKD system, quantum relays are very crucial for achieve the long-range, high-rate and large capacity QKD. However, the so-called quantum de-coherence effect will normally destroy the coherence in the quantum state and photons can propagate over long distance, at high speed, and with essentially interaction with their environment in atmospheric channel, thus they cause quantum transmission information loss. In the case, it is difficult to ensure the system security of satellite- ground QKD system. The proposal will focus on the security theory of satellite-ground QKD in quantum relay channels. The main research contents are described as follows. First, we investigate polarization coding scheme for subcarrier multiplexed QKD based on non-balanced Mach-Zehnder interferometer configuration, where the overall QKD can be substantially increased by relying on parallel sideband channels. Meanwhile, the polarization state of each sideband can be randomly and independently synthesized by controlling the phase difference of subcarriers. Therefore, suppression of de-coherence is essential to effective protection of satellite-relay QKD system that can establish de-coherence-free-subspaces to improve system security. Note that there are huge differences between these communication directions regarding the errors appearing in the channel, i.e., in relay-ground links, the atmosphere is part of the channel, where the effects of aerosols, the optical turbulence of the atmosphere on quantum communications, the finite size of the detectors, and beam spreading must be taken into account. Second, we study the improvement of quantum secure communication for satellite-ground QKD system based on the random characteristics of quantum relay channel, and solve the problems of the optical signal transmission (i.e., scintillation effect, random delay jitter, the synchronization and etc.) to reduce the effect of the system security. Note that the time synchronization and system timing jitter are essential to a practical QKD experiment, which can directly influence the quantum-bit-error-rate and the final key rate. Third, we extend quantum key distribution protocol based on quantum error-correcting codes or quantum error-avoiding codes, derive the extended protocols’ safety threshold formula for judging the wiretap, and provide the accurate judgment of other extended protocol for the unconditional security. These researches will bring new methods and techniques for information transmission and provide the theory basis and technical support to build internet architecture of satellite-ground cooperative communication.

将中继通信技术引入到星-地量子密钥分发系统中，理论上能实现远距离、高速大容量信息安全传输。然而，量子消相干和大气信道传输造成量子密钥分发的信息丢失，难以保证系统安全性。本项目拟开展基于量子中继的星-地量子密钥分发系统安全理论研究，主要研究内容包括：1)研究基于相位差极化编码的副载波复用量子密钥分发方案，克服卫星-中继站的量子密钥分发的消相干，提高系统安全。2)基于大气信道随机特性的星地中继量子密钥分发系统安全优化设计，拟解决中继站-地面经过大气信道引发光强闪烁效应、光信号传输的随机时延抖动以及光信号同步等问题，减少对系统安全性的影响。3)基于量子纠错编码/避错码，扩展单光子/多光子纠缠量子密钥分发协议，判别窃听的安全门限，减少量子密钥分发的过程中供窃听者造成信息传输安全性遭到破坏，为准确判断其它扩展协议的安全性提供依据。项目研究成果可为星-地量子信息系统安全及高速数据传输技术提供理论支撑。

将中继通信技术引入到星-地量子密钥分发系统中，理论上能实现远距离、高速大容量信息安全传输。然而，量子消相干和大气信道传输造成量子密钥分发的信息丢失，难以保证系统安全性。本项目开展了基于量子中继的星-地量子密钥分发系统安全理论研究，主要研究内容包括：1)研究了基于相位差极化编码的副载波复用量子密钥分发方案，设计了稳定子码理论及其相应的逻辑操作算子，提出了量子编译码新型构造方法，克服消相干并构造出量子避错码，并且设计出DFS基态任意线性组合的量子避错码，克服了卫星-中继站的量子密钥分发的消相干，提高系统安全。2)基于大气信道随机特性的星地中继量子密钥分发系统安全优化设计，建立了基于大气信道随机特性的信道模型，利用大气光传输理论研究了光的量子态在大气信道中的物理特性，解决了中继站-地面经过大气信道引发光强闪烁效应、光信号传输的随机时延抖动以及光信号同步等问题，减少对系统安全性的影响。并且提出了基于极化角动量与测量无关量子密钥分发协议实现星地远距离大气信道下量子密钥分发。3)基于量子纠错编码/避错码，扩展单光子/多光子纠缠量子密钥分发协议，判别窃听的安全门限，减少量子密钥分发的过程中供窃听者造成信息传输安全性遭到破坏，为准确判断其它扩展协议的安全性提供依据。4) 星地融合网络中的非正交多址接入技术研究。利用协作技术和认知技术将卫星网络和地面网络结合构建出星地融合网络，研究了引入5G NOMA技术的卫星通信网络、星地协作网络以及星地认知网络，通过NOMA技术在功率域的复用，充分利用了有限的时域和频域资源。5) 研究了星地量子通信网络密钥分发、可信中继、统一管控和灵活应用等关键技术。并且将这些技术应用到无线视频监控系统中多维信息获取、传输以及视频数据智能处理方法中，搭建了量子车载移动视频仿真实验平台。项目研究成果可为星-地量子信息系统安全及高速数据传输技术提供理论支撑。