泵浦光强度对纠缠光子品质的影响

纠缠源亮度和品质直接决定其作为量子信息处理资源的应用价值,研究参量转换过程中纠缠对的产生效率和品质随泵浦激光强度的变化关系对制备高品质纠缠源具有基础意义.利用参量下转换、极化后选择和符合计数技术,制备了Einstein-Podolsky-Rosen(EPR)偏振纠缠态.研究了泵浦激光强度对纠缠光子产生效率、对比度和保真度的影响.结果表明,随泵浦激光强度增大,纠缠对产生效率保持不变,也即纠缠源亮度随激光强度增大而线性增大;纠缠光子的对比度、保真度随激光功率增大而下降.     

双量子比特系统在Ising自旋链环境下的相干性冻结

本文研究双量子比特系统与Ising自旋链相耦合时的退相干动力学,解析地推导出相干性的演化规律。我们发现对一类特殊的初态,采用相对熵来度量的双量子比特系统的量子相干性在演化过程中存在冻结现象。同时,在弱耦合的情形下,量子相干性在Ising链的临界点附近存在突变现象。     

量子变换理论及其应用概述

概括地介绍了量子变换理论的基本思想,并就这一基本理论在指数上二次型的正规与反正规乘积表示、二次型哈密顿量的配分函数和波函数,以及量子信息中连续变量系统的纠缠度和保真度的计算做了简要的说明。     

各向异性n模耦合谐振子的精确求解

利用量子变换理论,极其简洁地给出了种向异性耦合谐振子的能谱,从而提出了一种普遍的方法。     

原子偶极压缩的相干控制和Cauchy-Schwarz不等式的破坏

通过研究孤立二能级原子与双模纠缠相干光场的相互作用,分析了体系中原子偶极压缩量子效应的时间演化规律.体系中作用场模的性质决定了原子偶极压缩程度;同时定义了体系的Cauchy-Schwarz不等式破坏参数ΔV,研究了不同条件下参数ΔV的时间演化特性,Cauchy-Schwarz不等式破坏程度和体系中所具有的非经典特性是一致的;即可以通过调控相干场参数来远程控制体系中的非经典特性. 关键词： 量子光学 双模纠缠相干态 偶极压缩效应 Cauchy-Schwarz 不等式     

Relative entropy as a measure of entanglement for Gaussian states

In this paper, we derive an explicit analytic expression of the relative entropy between two general Gaussian states. In the restriction of the set for Gaussian states and with the help of relative entropy formula and Peres--Simon separability criterion, one can conveniently obtain the relative entropy entanglement for Gaussian states. As an example, the relative entanglement for a two-mode squeezed thermal state has been obtained.     

ENERGY SPECTRUM AND WAVE FUNCTION FOR MULTI-MODE COUPLED NON-IDENTICAL HARMONIC OSCILLATORS

By means of the linear quantum transformation theory, we consisely derive the exact solution including energy spectrum and wave function for multi-mode coupled non-identical harmonic oscillators.     

广义Greenberger-Horne-Zeilinger态纠缠度和Bell型不等式实验

利用制备的三光子偏振广义Greenberger-Horne-Zeilinger纠缠态,测量了三体纠缠度、Svetlichny不等式和广义Greenberger-Horne-Zeilinger态的密度矩阵.根据密度矩阵计算了三体纠缠度,测量得到了广义Greenberger-Horne-Zeilinger纠缠态的纠缠和非定域性之间的关系.结果表明:在实验误差范围内,三体纠缠度的实验测量值和理论值一致;Svetlichny算符的期望值和理论计算结果具有较好的一致性;体系非定域特性和体系的纠缠程度密切相关,当纠缠度减小时,非定域性减弱.     

Frozen Quantum Coherence for a Central Two-Qubit System in a Spin-Chain Environment

We investigate the dynamics of coherence for a central two-qubit system coupled to an XY spin chain with the Dzyaloshinsky–Moriya interaction. It is found that a sudden transition of coherence exists near the critical point in the weak-coupling case, and an oscillatory envelope appears in the strong-coupling case. In both cases the freezing phenomenon of coherence can be found.     

Dynamics of the entanglement witness for three qubits in common environment

In the measurement-based model of quantum computing, a one-way quantum computer consisting of many qubits can be immersed in a common environment as a simple decoherence mechanism. This paper studies the dynamics of entanglement witness for 3-qubit cluster states in the common environment. The result shows that environment can induce an interesting feature in the time evolution of the entanglement witness: i.e., the periodical collapse and revival of the entanglement dynamics.