玻色-爱因斯坦凝聚中的量子涡旋

<正>玻色-爱因斯坦凝聚(BEC)是物理学中弥足珍贵的一种宏观量子现象,是指极低温度下(nK量级)玻色子在能量最低量子态的聚集,被认为是物质除固态、液态和气态之外的第四种存在形态。从1925年爱因斯坦预言其存在后,就一直吸引着理论和实验的研究。关于玻色-爱因斯坦凝聚的突破性进展明确地展示了其与超流和超导等重要物理现象     

基于线性与非线性干涉仪的量子精密测量研究进展

量子精密测量根据量子力学的基本原理,利用光、原子、磁之间的相互作用对待测物理量进行测量.随着实验条件和技术的成熟,如何利用干涉仪进一步提高位相信号这一物理量的测量精度从而打破散粒噪声的限制、突破标准量子极限并逼近海森伯极限成为研究的前沿课题.本文阐述了利用线性干涉仪(包括原子/光子干涉仪)与非线性干涉仪调用不同阶段的量子资源在测量过程中提高参数评估精度的几种方法,通过向干涉仪中输入非经典态来实现高精度测量,如压缩态、双数态、NOON态等,还介绍了为直接观测量子态而发展出的弱测量及其在非厄米系统中的应用和为消除参数之间精度制衡而提出的多参数测量.最后,对几种测量方法进行了分析比较,并展望了量子精密测量的发展前景.     

Dynamics of magnetization in ferromagnet with spin-transfer torque

We review our recent works on dynamics of magnetization in ferromagnet with spin-transfer torque. Driven by constant spin-polarized current, the spin-transfer torque counteracts both the precession driven by the effective field and the Gilbert damping term different from the common understanding. When the spin current exceeds the critical value, the conjunctive action of Gilbert damping and spin-transfer torque leads naturally the novel screw-pitch effect characterized by the temporal oscillation of domain wall velocity and width. Driven by space- and time-dependent spin-polarized current and magnetic field, we expatiate the formation of domain wall velocity in ferromagnetic nanowire. We discuss the properties of dynamic magnetic soliton in uniaxial anisotropic ferromagnetic nanowire driven by spin-transfer torque, and analyze the modulation instability and dark soliton on the spin wave background, which shows the characteristic breather behavior of the soliton as it propagates along the ferromagnetic nanowire. With stronger breather character, we get the novel magnetic rogue wave and clarify its formation mechanism. The generation of magnetic rogue wave mainly arises from the accumulation of energy and magnons toward to its central part. We also observe that the spin-polarized current can control the exchange rate of magnons between the envelope soliton and the background, and the critical current condition is obtained analytically. At last, we have theoretically investigated the current-excited and frequency-adjusted ferromagnetic resonance in magnetic trilayers. A particular case of the perpendicular analyzer reveals that the ferromagnetic resonance curves, including the resonant location and the resonant linewidth, can be adjusted by changing the pinned magnetization direction and the direct current. Under the control of the current and external magnetic field, several magnetic states, such as quasi-parallel and quasi-antiparallel stable states, out-of-plane precession, and bistable states can be realized. Th     

规范势下正方形格点超导量子比特电路中的量子态输运

借助于电感型耦合器产生人造规范势(有效磁通),本文研究了正方形传输子量子比特模型中的量子态输运性质.理论计算发现,单粒子本征态与单空穴本征态具有相同的本征能谱,并且相同能量下,两者的平均粒子流与平均空穴流受有效磁通正弦调制后互为相反数.当初态为占据一个格点的单粒子与单空穴时,如果系统时间反演对称(有效磁通为4π的整数倍),单粒子与单空穴的含时波函数各分量相等,否则不等.分析证明,以上计算结果是由于对体系哈密顿量的粒子-空穴操作等价于对其做时间反演.此外还发现,有效磁通为π时,单粒子或单空穴只在初始比特与两个相邻比特之间输运,有效磁通为0时,单粒子或单空穴通过两个相邻比特输运到对角比特,然后再反向输运;无论有效磁通如何取值,两者具有相同的平均(粒子或空穴)流和格点占据概率.     

自旋-轨道耦合二分量玻色-爱因斯坦凝聚系统的孤子解

在旋量玻色-爱因斯坦凝聚体中,孤子态作为宏观量子效应的典型状态,可以通过自旋-轨道耦合进行调控,这使得对自旋-轨道耦合玻色-爱因斯坦凝聚体中孤子的研究成为近年来超冷原子领域研究的重要课题之一.本文研究了描述一维自旋-轨道耦合二分量玻色-爱因斯坦凝聚体Gross-Pitaevskii方程的精确求解,利用直接假设及可积约化方法,给出了系统多种类型的孤子解,讨论了相应的孤子动力学以及自旋-轨道耦合效应对系统的量子磁化和自旋-极化态的影响.     

混价格子模型的一些精确结果

用Bethe ansatz方法构造了混价格子模型Hamilton量的精确本征态,由周期边界条件获得了Bethe ansatz方程.结果表明混价格子模型是完全可积的.     

格林函数的有限形式法中微分方程之解的证明

本文通过对静电场格林函数分离变量得到非齐次常微分方程，判断其解及解存在的条件，完善了电动力学［１］提到的格林函数的有限形式法．     

An important property of entanglement： pairwise entanglement that can only be transferred by an entangled pair

Based on the calculation of all the pairwise entanglements in the n （n ≤ 6）-qubit Heisenberg XX open chain with system impurity, we find an important result： pairwise entanglement can only be transferred by an entangled pair. The non-nearest pairwise entanglements will have the possibility to exist as long as there has been even number of qubits in their middle. This point indicates that we can obtain longer distance entanglement in a solid system.     

Generation of Long-Distance Entanglement in Spin System

We propose two schemes to produce long-distance entanglement in a spin chain. The first is based on a controllable interaction system, one starts from an entangled kernel and adds weaken interaction spins to the boundary sites step by step, then the entanglement will be extended longer and longer and its value is equal to that of its kernel. The second is based on a uniform interaction （J） system with a bulk magnetic field （B） that is absent for the boundary qubits, as long as B/J 〉 5, one can obtain near perfect long distance entanglement. Ultra-low temperature is needed in both schemes.     

Particle-hole bound states of dipolar molecules in an optical lattice

We investigate the particle-hole pair excitations of dipolar molecules in an optical lattice, which can be described with an extended Bose-Hubbard model. For strong enough dipole-dipole interaction, the particle-hole pair excitations can form bound states in one and two dimensions. With decreasing dipole-dipole interaction, the energies of the bound states increase and merge into the particle-hole continuous spectrum gradually. The existence regions, the energy spectra and the wave functions of the bound states are carefully studied and the symmetries of the bound states are analyzed with group theory. For a given dipole-dipole interaction, the number of bound states varies in momentum space and a number distribution of the bound states is illustrated. We also discuss how to observe these bound states in future experiments.