An efficient and practical post-processing technique based on reverse reconciliation for continuous variable quantum key distribution is proposed and simulated with low-density parity check (LDPC) codes. MultiLevel Coding/ MultiStage Decoding, which fully utilizes optimization technique such as vector quantization and iterative decoding and the optimal channel coding most close to the Shannon limit, was used to realize efficient reverse reconciliation algorithm. Simulation results showed that the proposed method can improve the secure key distribution rate to 2.2 kb/s and the coding efficiency to 0.89 over 20 km in single-mode optical fiber. Moreover, there still is room for much improvement.
LU ZhiXin 1,2 , YU Li 1,2 , LI Kang 1,2 , LIU BingCan 1,2,3 , LIN JianGui 1,2 , JIAO RongZhen 1,2 & YANG BoJun 1,21 School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China
In the asymmetric and symmetric nonlinear-metal-nonlinear dielectric structures, this paper studies the analytic dispersion relation for surface plasmon in a system consisting of a thin metallic film covered on two sides media of intensity-dependent refractive indexes by applying a generalised first integral approach. Especially in the symmetric waveguide structure, two possible modes can exist： the odd mode and the even mode. The dispersion relations of the two modes are obtained. Due to the nonlinear dielectric, the squared magnitude of the electric field at the interface appears and alters the dispersion relations. Numerical results are compared to those from a certain approximate treatment.
Surface plasmon polaritons (SPPs) are the combined electron oscillations and electromagnetic waves propagating along the interface between a conductor and a dielectric. Recently Huck et al. [Huck A, et al. Phys Rev Lett, 2009, 102: 246802] proved that SPPs can be in a squeezed state, and the squeezed surface plasmons can propagate in a gold waveguide. In this paper, we introduce a quantum mechanical description of the squeezed surface plasmons at first, and discuss the influence of the waveguide losses on the squeezed surface plasmons.
We propose a practical entanglement concentration protocol （ECP） for a hybrid entangled state using quantum dots and a microcavity coupled system. A hybrid less-entangled state can he concentrated to a most-entangled state with a certain probability using only one ancillary single photon. Moreover, using this protocol, we can also concentrate an arbitrary three-particle less-entangled W state using two ancillary photons and classical communication. The proposed protocols provide us with a useful method to concentrate less-entangled states, which can he implemented with current technology.
针对实用的量子密钥分配(QKD)系统是基于强衰减的弱激光脉冲作为单光子源,光子数分束攻击极大限制了通信双方在非理想条件下QKD的传输距离和密钥生成率,采用大数定律对诱惑态协议中单光子的计数率、单光子增益和误码率分别进行统计涨落分析,利用双诱惑态比较了1310 mn和1550 nm条件下,编码脉冲的长度为(N=10°-N=10^(12))实际QKD协议中密钥的生成率与安全传输距离之间的关系、安全传输距离随编码长度的变化的关系,得出脉冲编码长度增大到N=10^(12)时,密钥的最大安全传输距离为135 km.
In this review article,we will review the recent process of quantum communications.In the past decades,there are many developments in quantum communication,for instance,quantum key distribution,quantum teleportation,quantum secure direct communication,deterministic secure quantum communication,quantum secret sharing and so on.And we focus our attention on the recent developments in quantum communication protocols.
