Quantitative Accuracy Assessment and Optimization of SPECT Geometrical Calibration

Accurate geometrical calibration is critical to obtaining high resolution and artifact free reconstructed images for modern animal single photon emission computed tomography(SPECT) systems.Although there have been many published works on the calibration of various SPECT systems,few studies have been done to evaluate the efficacy of the proposed calibration methods in a quantitative manner.This paper presents a numerical method to assess both the uniqueness and the quantitative accuracy of SPECT calibration,...     

含能流的三比特伊辛自旋链中的基态纠缠

研究了含能流的三比特伊辛自旋链中的基态纠缠。在体系中引入能流后,磁场的变化将会导致系统进入能流相。基态纠缠在相变临界点处发生突变,两粒子之间的纠缠由于能量的流动而得到增强。     

SPECT局部重建中小波去噪方法研究

针对单光子发射断层成像技术中全局图像重建时间过长的问题,提出了局部重建的思想,同时为了提高局部重建图像的质量,需要在局部重建之前,对投影图像进行噪声去除.利用基于小波变换的复数改进二元萎缩相关去噪法,对噪声投影图进行处理,并利用局部重建算法进行图像的局部重建,在保留图像细节的同时,降低了图像噪声,缩短了重建时间.利用均方误差评价标准,对去噪结果进行评测,结果表明:在局部重建中,利用该方法进行去噪处理具有良好的效果.     

Entanglement dynamics and transfer in a double Jaynes-Cummings model

We study the entanglement dynamics for a double Jaynes-Cummings model where two entangled atoms A and B locally interact with independent cavities a and b, respectively, but there are no interactions between locations Aa and Bb. We point out that there exists a parameter range in which simultaneous pairwise entanglement sudden death (ESD) for remote parties, i.e. AB, ab, Ab and Ba, may occur. We show that during this simultaneous ESD period various multipartite entanglement can be created. Our results imply that the pairwise entanglement between two independent locations may be transferred into other multipartite forms which account for the correlations between the two independent locations.     

Single photon response of superconducting nanowire single photon detector

Single photon detection is one of the key technologies for quantum key distribution in quantum communication. As a novel single photon detection technology, superconducting nanowire single photon detector (SNSPD) surpasses conventional semiconducting single photon detectors with high count rate and low dark count rate. In this article, we introduce SNSPD fabricated from NbN ultrathin superconducting film and lab-based SNSPD system. The characteristics of single photon response pulse of SNSPD are analyzed in detail. Also discussed is the relationship between waveform of single photon response and system bandwidth. Circuit model is made to analyze the performance of SNSPD. The simulation result agrees well with the experimental data. Those results are valuable for understanding the mechanism of SNSPD and building future SNSPD system for quantum communication.     

采用纠缠私钥实现多方量子隐蔽通信

提出一种新的量子多方隐蔽通信方案,根据伪随机序列从共享纠缠密钥集中选择随机子集用于多方加密方案,利用量子信道噪声的掩盖将敏感信息伪随机旋转并伪装到量子纠错码中. 利用伪随机序列选择共享密钥子集补构造侦测子集,采用判断典型错误机制实现密钥的循环使用. 相比于其他隐蔽通信方案密钥消耗量大的缺点,该方案显著降低了密钥消耗,优化了共享密钥子集补判断典型错误的检测机制检测窃听的功能. 分析了抵抗特洛伊木马攻击的能力.     

三模系统二阶非线性诱导的非传统光子阻塞

基于三模二阶非线性系统, 推导一个Hamilton量. 在双模驱动的条件下, 先用该Hamilton量与常规非厄米Hamilton方法, 得到发生非传统阻塞的最佳解析条件, 再通过求解主方程的稳态解及二阶关联函数, 得到发生阻塞的数值解.     

PT对称Bell态的经典纠缠与CPT纠缠

研究4个宇称\|时间(PT)对称Bell态在经典Hermite条件下的纠缠问题. 结果表明: 在4个PT对称Bell态中, |Φ_-〉和|Ψ_-〉仍为经典量子态, 且在经典量子Hermite内积下仍为最大纠缠态; |Φ₊〉和|Ψ₊〉不再总是经典量子态, 将其在Hermite内积下进行规范化后的经典量子态也不再总是Hermite内积下的最大纠缠态.     

用多个光子晶体实现量子纠缠态的稳定性

量子纠缠态的纠缠度随传播距离增加或外界干扰而变小,  在光与环境相互作用的退相干效应下,  可使纠缠度降低或不再纠缠.  基于此, 设计一组一维光子晶体, 当两光子或三光子的纠缠光通过该组光子晶体, 且叠加参数c1=0.03~0.98时, 纠缠度E=0.8~1, 从而使量子纠缠态可远距离传输, 更好地实现量子通信.     

利用动力学去耦合脉冲增大和调节量子相干性和三体纠缠

本文研究了动力学去耦合脉冲对腔量子电动力学系统中量子相干性, 量子失谐和量子纠缠的影响, 发现动力学去耦合脉冲不仅能够增大系统中两原子之间的量子相干性, 同时也能增大它们之间非经典关联（量子失谐和量子纠缠）. 同时, 凭借迹距离的方法, 探讨了动力学去耦合脉冲增大两原子之间量子相干性的原因, 通过探究可以看出动力学去耦合脉冲能够控制和加速量子信息从其他子系统回流到两个原子中去, 并减少两原子子系统和其他子系统之间的量子信息流动, 从而增加两原子间的量子相干性和非经典关联. 最后, 利用保真度的方法研究了系统中三体纠缠出现的情况, 结果显示在不同的时间, 系统中会出现三体纠缠, 特别值得指出的是, 可以通过动力学去耦合脉冲来调节和增加系统中三体纠缠出现的时间.