Non-Orthogonality Measure for a Collection of Pure Quantum States

Modern optical communication technology can realize a large-scale multilevel (or M-ary) optical signal. Investigating the quantum mechanical nature of such a large-scale M-ary optical signal is essential for a unified understanding of quantum information science and optical communication technology. This article focuses on the quantum-mechanical non-orthogonality for a collection of pure quantum states and proposes a non-orthogonality index based on the least squares error criterion in quantum detection theory. First, we define the index for linearly independent signals, and the proposed index is analyzed through numerical simulations. Next, the index is applied to a highly large-scale M-ary phase-shift keying (PSK) coherent state signal. Furthermore, the index is compared with the capacity of the pure state channel with the PSK signal. As a result, it is shown that a highly large-scale M-ary PSK coherent state signal exhibits a quantum nature even when the signal transmission power is very high. Thus, the theoretical characterization of a highly large-scale M-ary coherent state signal based on the proposed index will be the first step toward a better understanding of cutting-edge optical communication technologies such as the quantum stream cipher Y00.     

城市路径下激光光强起伏特性测量及链路余量估算

 在城市环境下进行了3.5 km的激光大气传输实验。实验中对光强起伏和到达角起伏进行了同步测量,分析了接收光强起伏的统计特性以及传输路径上大气折射率结构常数的特性。基于实验结果,对自由空间光通信中不同闪烁指数下的衰落冗余以及不同探测阈值下的衰落概率进行了估算,从而为空间光通信系统的设计提供可靠的实验基础。     

时域相位光码分多址系统性能分析

给出了时域相位光码分多址系统(OCDMA)的噪声模型,提出了由码间串扰(ISI)所引起的自差拍噪声(SB)概念.利用鞍点近似法分析了多址干扰(MAD、码间串扰、自差拍等噪声对系统性能的影响,给出了系统误码率公式.对最佳门限接收系统以及采用光硬件限幅器的系统性能进行了仿真研究.表明"1"码的误判概率是影响系统的决定性因素.也是开关键控(OOK)系统难以克服的主要问题.最后给出一种采用双编/解码器平衡检测系统的原理框图,分析其性能,并与传统OOK系统比较,结果表明其性能有较大的提高.     

Effects of Environmental and Electric Perturbations on the pKa of Thioredoxin Cysteine 35: A Computational Study

Here we present a theoretical-computational study dealing with the evaluation of the pKa of the Cysteine residues in Thioredoxin (TRX) and in its complex with the Thioredoxin-interacting protein (TXNIP). The free energy differences between the anionic and neutral form of the Cysteine 32 and 35 have been evaluated by means of the Perturbed Matrix Method with classical perturbations due to both the environment and an exogenous electric field as provided by Molecular Dynamics (MD) simulations. The evaluation of the free energies allowed us to show that the effect of the perturbing terms is to lower the pKa of Cysteine 32 and Cysteine 35 with respect to the free amino-acid. On the other hand, in the complex TRX-TXNIP, our data show an enhanced stabilization of the neutral reduced form of Cys 35. These results suggest that external electric stimuli higher than 0.02 V/nm can modulate the Cysteine pKa, which can be connected to the tight regulation of the TRX acting as an antioxidant agent.