针对空-水量子密钥分发(Quantum Key Distribution,QKD), 综合考虑海风影响、泡沫覆盖的不规则海面、空-水信道复杂多变性和量子偏振态多重散射过程, 建立了非均匀空-水信道复合模型。据此完善了空-水QKD系统量子误码率理论模型, 并采用偏振矢量蒙特卡罗算法模拟, 详细分析了不同海洋环境下非均匀空-水信道光量子传输性能, 及空-水QKD整体传输性能。结果表明: 清澈海水条件下的非均匀空-水信道可实现水下百米量级的密钥分发, 但风速和传输距离的增大都会导致光子退偏比增大, 保真度减小, 偏振误码率增加; 同时风速和泡沫层厚度的增大也会造成空-水QKD系统量子误码率上升, 密钥生成率和传输距离下降, 且随信号波长的增加这两者也会增加, 在波长为532 nm, 信道由最佳(无风无泡沫)变至最差(暴风且泡沫层为6 cm)时, 水下传输距离由1208 m缩减至85 m, 基本能保障水下航行器百米级的安全潜深, 而采用拖拽浮标等措施又可进一步增加空-水QKD的安全距离。由此验证了泡沫覆盖不规则海面下非均匀空-水信道诱骗态QKD的可行性, 对未来空-水一体量子通信链路的实现具有参考价值。

Based on the orbital angular momentum and pulse position modulation, we present a novel passive measure-ment-device-independent quantum key distribution (MDI-QKD) scheme with the two-mode source. Combining with the tight bounds of the yield and error rate of single-photon pairs given in our paper, we conduct performance analysis on the scheme with heralded single-photon source. The numerical simulations show that the performance of our scheme is significantly superior to the traditional MDI-QKD in the error rate, key generation rate and secure transmis-sion distance, since the application of orbital angular momentum and pulse position modulation can exclude the ba-sis-dependent flaw and increase the information content for each single photon. Moreover, the performance is im-proved with the rise of the frame length. Therefore, our scheme, without intensity modulation, avoids the source side channels and enhances the key generation rate. It has greatly utility value in the MDI-QKD setups.

为解决多幅分块图像在图像重建和加密等方面存在运算量巨大的局限性，提出了基于压缩感知和正交调制实现图像分块重建的新方法。该方法将单幅图像按需要均分为若干块，对于每一个块图像分别进行压缩感知的采集过程，再将采集的测量值和正交基矩阵相乘完成正交调制。当需要从总数据中恢复部分信息时，只要乘以与待恢复部分相应的正交基矩阵的转置，便可提取出需要恢复的块图像测量值。最后利用正交匹配追踪算法进行重建运算。实验结果表明，在采样率为30%左右时，可以精确重建出原始图像，且加密安全性高。

A measurement-device-independent quantum key distribution (MDI-QKD) method with an air-water channel is researched. In this method, the underwater vehicle and satellite are the legitimate parties, and the third party is at the airwater interface in order to simplify the unilateral quantum channel to water or air. Considering the condition that both unilateral transmission distance and transmission loss coefficient are unequal, a perfect model of the asymmetric channel is built. The influence of asymmetric channel on system loss tolerance and secure transmission distance is analyzed. The simulation results show that with the increase of the channel’s asymmetric degree, the system loss tolerance will descend, one transmission distance will be reduced while the other will be increased. When the asymmetric coefficient of channel is between 0.068 and 0.171, MDI-QKD can satisfy the demand of QKD with an air-water channel, namely the underwater transmission distance and atmospheric transmission distance are not less than 60 m and 12 km, respectively.

With a heralded single photon source (HSPS), a measurement-device-independent quantum key distribution (MDIQKD) protocol is proposed, combined with a three-intensity decoy-state method. HSPS has the two-mode characteristic, one mode is used as signal mode, and the other is used as heralded mode to reduce the influence of the dark count. The lower bound of the yield and the upper bound of the error rate are deduced and the performance of the MDI-QKD protocol with an HSPS is analyzed. The simulation results show that the MDI-QKD protocol with an HSPS can achieve a key generation rate and a secure transmission distance which are close to the theoretical limits of the protocol with a single photon source (SPS). Moreover, the key generation rate will improve with the raise of the senders’ detection efficiency. The key generation rate of the MDI-QKD protocol with an HSPS is a little less than that of the MDI-QKD protocol with a weak coherent source (WCS) in the close range, but will exceed the latter in the far range. Furthermore, a farther transmission distance is obtained due to the two-mode characteristic of HSPS.

Considering the air-water interface and ocean water’s optical attenuation, the performance of quantum key distribution (QKD) based on air-water channel is studied. The effects of photons’ various incident angles to air-water interface on quantum bit error rate (QBER) and the maximum secure transmission distance are analyzed. Taking the optical attenuation of ocean water into account, the performance bounds of QKD in different types of ocean water are discussed. The simulation results show that the maximum secure transmission distance of QKD gradually reduces as the incident angle from air to ocean water increases. In the clearest ocean water with the lowest attenuation, the maximum secure transmission distance of photons far exceeds the the working depth of underwater vehicles. In intermediate and murky ocean waters with higher attenuation, the secure transmission distance shortens, but the underwater vehicle can deploy other accessorial methods for QKD with perfect security. So the implementation of OKD between the satellite and the underwater vehicle is feasible.

Combining heralded pair coherent state (HPCS) with passive decoy-state idea, a new method is presented for quantum key distribution (QKD). The weak coherent source (WCS) and heralded single photon source (HSPS) are the most common photon sources for state-of-the-art QKD. However, there is a prominent crossover between the maximum secure distance and the secure key generation rate if these two sources are applied in a practical decoy-state QKD. The method in this paper does not prepare decoy states actively. Therefore, it uses the same experimental setup as the conventional protocol, and there is no need for a hardware change, so its implementation is very easy. Furthermore, the method can obtain a longer secure transmission distance, and its key generation rate is higher than that of the passive decoy-state method with WCS or HSPS in the whole secure transmission distance. Thus, the limitation of the mentioned photo sources for QKD is broken through. So the method is universal in performance and implementation.

功率控制是无线数据网络中资源管理的关键技术。为使无线数据网络中非 合作博弈功率控制算法得到帕累托改进, 将斯塔克尔博格博弈引入到无线数据网络功率控制算法中, 使所有系统终端都工作在最佳的等信干比下, 提出一个基于斯塔克尔博格博弈的分布式功率控制算法, 并进行了数值仿真。仿真结果表明, 该算法明显提高了系统的性能, 使系统终端具有相对较高的效用和较低的发射功率, 并使得无线网络资源的 使用更加合理和公平, 同时算法拥有较好的收敛性。

Considering fluctuant dark count rate in practical quantum key distribution (QKD) system, a new decoy-state method with one vacuum state and one weak decoy state is presented based on a heralded single photon source (HSPS). The method assumes that the dark count rate of each pulse is random and independent. The lower bound of the count rate and the upper bound of the error rate of a single photon state are estimated. The method is applied to the decoy-state QKD system with and without the fluctuation of dark count rate. Because the estimation of the upper bound of a single photon state’s error rate is stricter, the method can obtain better performance than the existing methods under the same condition of implementation.

指出多小区无线数据系统中基于非合作博弈的功率控制算法的纳什均衡不是帕累托最优的。 提出一种新的适用于多小区无线数据网络的基于最佳等信干比的功率控制算法,使系统中每个小 区的终端都工作在最佳等信干比下。仿真结果表明,该算法明显提高了系统的性能,使系统终端具 有相对较高的效用和较低的发射功率,并使得无线网络资源的使用更加合理和公平。