基于准单光子光源HSPS(heralded single photon source),推导了非正交(SARG04)三诱惑态(真空态和2个弱光强态)量子密钥分配方案。为了降低实现难度,将2个弱光强态合并,提出了简化的二诱惑态方案(真空态和一个弱光强态)。此方案将主动诱惑态方案和被动诱惑态方案相结合,不舍弃接收者检测结果中发送端探测器没有响应的脉冲集合,而是用来估计参量和生成密钥。数值仿真表明,被动诱惑态思想的加入,提高了密钥生成效率;二诱惑态方案的密钥生成效率非常趋近于无穷诱惑态方案的理论极限值;在实现难度相同的条件下,SARG04协议的密钥生成效率和传输距离都高于BB84协议。
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.
A hybrid decoding algorithm is proposed for nonbinary low-density parity-check （LDPC） codes, which combines the weighted symbol-flipping （WSF） algorithm with the fast Fourier trans- form q-ary sum-product algorithm （FFT-QSPA）. The flipped position and value are determined by the symbol flipping metric and the received bit values in the first stage WSF algorithm. If the low- eomplexity WSF algorithm is failed, the second stage FFT-QSPA is activated as a switching strategy. Simulation results show that the proposed hybrid algorithm greatly reduces the computational complexity with the performance close to that of FFT-QSPA.
