Thermal Entanglement of Anisotropic XY Chains in a Transverse Field

By using the concept of concurrence, we numerically investigate the thermal entanglement between any two nearest-neighbour spins in uniform and periodic anisotropic XY chains in a transverse field at finite temperature T. It is found that the entanglement has more than one critical temperatures on some parameter regions for uniform and periodic chains. We also discuss the behaviour of the thermal entanglement at the vicinity of quantum phase transition of periodic anisotropic XY chains and find that a11 the derivatives aλC have similar behaviour as that of the uniform chain.     

On Effectiveness of Protocol Creating Maximum Entanglement of Two Charge-Phase Qubits by Cavity Field

We revisit the protocols to create maximally entangled states between two Josephson junction （33） charge phase qubits coupled to a microwave field in a cavity as a quantum data bus. We analyze a novel mechanism of quantum decoherence due to the adiabatic entanglement between qubits and the data bus, the off-resonance microwave field. We show that even if the variable of the data bus can be adiabatically eliminated, the entanglement between the qubits and data bus remains and can decohere the superposition of two-particle state. Fortunately we can construct a decoherencefree subspace of two-dimension to against this adiabatic decoherence. To carry out the analytic study for this decoherence problem, we develop Frohlich transformation to re-derive the effective Hamiltonian of these systems, which is equivalent to that obtained from the adiabatic elimination approach.     

Genuine tripartite entanglement and quantum phase transition

A new simplified formula is presented to characterize genuine tripartite entanglement of （2 2 n）-dimensional quantum pure states. The formula turns out equivalent to that given in （Quant. Inf. Comp. 7（7） 584 （2007））, hence it also shows that the genuine tripartite entanglement can be described only on the basis of the local （2 2）-dimensional reduced density matrix. In particular, the two exactly solvable models of spin system studied by Yang （Phys. Rev. A 71 030302（R） （2005）） are reconsidered by employing the formula. The results show that a discontinuity in the first derivative of the formula or in the formula itself of the ground state just corresponds to the existence of quantum phase transition, which is obviously different from the concurrence.     

Entropy evolvement properties in a system of Schrodinger cat state light field interacting with two entangled atoms

The field entropy can be regarded as a measurement of the degree of entanglement between the light field and the atoms of a system which is composed of two-level atoms initially in an entangled state interacting with the Schr\"{o}dinger cat state. The influences of the strength of light field and the phase angle between the two coherent states on the field entropy are discussed by using numerical calculations. The result shows that when the strength of light field is large enough the field entropy is not zero and the degrees of entanglement between the atoms and the three different states of the light fields are equal. When the strength of the light field is small, the degree of entanglement is maximum in a system of the two entangled atoms interacting with an odd coherent state; it is intermediate for a system of the two entangled atoms interacting with the Yurke--Stoler coherent state, and it is minimum in a system of the two entangled atoms interacting with an even coherent state.     

聚醋酸乙烯酯/聚丙烯酸甲酯互穿网络聚合物的平衡溶胀行为及网络间的互穿缠结

本文在Thiele-Cohen模型的基础上,引入聚合物Ⅰ/聚合物Ⅱ/溶剂三元体系的作用参数,推导了一般均相互穿网络聚合物(IPN)体系的溶胀方程,将聚醋酸乙烯酯/聚丙烯酸甲酯(PVAc/PMA)IPN在丙酮中平衡溶胀度λ的理论计算值与实验值做了比较,方程经Siegfried修正后,能较好地描述一般均相IPN体系的溶胀行为,并观察到在IPN的网络之间存在着明显的互穿缠结效应。     

部分解缠结聚苯乙烯在纳米孔道中的受限流动行为研究

高分子的长链特征使其对纳米到微米尺度的空间受限非常敏感,也是当前微电子电路、微器件传感器等领域材料制造及其工艺研发中的关键之一.本工作从不同缠结程度的窄分布聚苯乙烯出发,以不同孔径的阳极氧化铝模板为二维受限空间,研究了高分子熔体在其中的纳米受限流动行为.我们发现,缠结程度低的聚苯乙烯在受限流动初期显著快于本体,后因缠结恢复逐渐降至与本体相当,缠结恢复时间尺度与宏观流变实验获得的缠结恢复时间处于同一个数量级.我们认为缠结程度降低后流动的加速来源于受限状态时在压力梯度推动下高分子链通过蛇行进入孔道的速率加快;同时受限链段由于非平衡构象增多而重排更加频繁,导致强受限程度下部分解缠结样品的缠结恢复加快.本文希望通过对链缠结在高分子链进入受限空间中作用的探索,为受限态高分子复合材料的加工工艺提供新的理解.     

分子链缠结对核-壳结构复合凝胶非均匀变形行为的影响

凝胶分子形成凝胶网络时,分子链段间会相互缠绕形成物理交联,显著影响其力学行为.为研究凝胶分子链段间相互缠结形成的物理交联对核壳结构复合凝胶变形行为与溶剂分布的影响,基于slip-link链缠结模型和张量推导建立核壳结构复合凝胶变形过程的一般数学表达式.结果表明：受刚性核影响,凝胶壳的拉伸是各向异性的,凝胶壳内溶剂的分布也是非均匀的,由内向外呈非线性变化,溶剂在凝胶内的扩散不满足菲克扩散定律;分子链缠结度越高凝胶壳的径向和周向伸长比越低,凝胶的溶胀率也越低.     

Entanglement Evolution of Two-Coupled Spins in a Time-Dependent Rotating Magnetic Field

We study the dynamics evolution of a two-qubit Heisenberg XXX spin chain under a time-dependent rotating magnetic field. Based on the algebraic structure of the non-autonomous system, the exact solution of the Schrodinger equation is obtained by using the method of algebraic dynamics. Based on the time-dependent analytical solution, we further study the entanglement evolution between the two coupled spins for different initial states, and find that the entanglement is determined by the coefficients of the initial state and the coupling constant J of the system.     

缠结高分子液体在管中挤出胀大动力学理论：一组新的增长和最终挤出胀大比方程

基于O-W-F本构方程和自由回复机制，从Poioeuille流出发建立了一种新的缠结高分子液体挤出胀大动力学理论，该理论能有效地预测高分子流体的动静态挤出胀大行为同高分子粘弹性参数和成型条件间的相关性. 基于稳态剪切量可分解为自由“回复线团”和“不可回复热耗”两部分事实，定义了一个稳态剪切下自由“回复线团”和“不可回复热耗”的配分函数和它们两者间分配指数上可回复和不可回复构象分数，从而在理论上得到了瞬时、推迟和最终三者可回复形变量和可回复线团量同配分函数、分配指数上可回复构象分数、分子粘弹性参数和成型条件     

Entanglement-Assisted Classical Capacity of a Generalized Amplitude Damping Channel

The entanglement-assisted capacity of a generalized amplitude damping channel is investigated by using the properties of partial symmetry and concavity of mutual information. The numerical and analytical results of the entanglement-assisted capacity are obtained under certain conditions. It is shown that the entanglement-assisted capacity depends on the channel parameters representing the ambient temperature and dissipation, and the prior entanglement between sender and receiver can approximately double the classical capacity of the generalized amplitude damping channel.