双势阱中冷原子的关联隧穿

研究了在不同的相互作用和隧穿耦合强度比值情况下双势阱中冷原子的隧穿现象.两格点Bose-Hubbard模型不能完全解释实验.为此,对此模型做了高阶修正.取双势阱的基态和第一激发态作基矢,写出哈密顿量的表示,解释了用两格点Bose-Hubbard模型分析实验时参数不能定量符合的原因.另外,通过计算两阱中原子纠缠度的变化,结合三态上原子布居数分布,直观描述了整个隧穿过程.     

一维双组分玻色-爱因斯坦凝聚体系的量子隧穿特性

利用双模近似方法研究了一维双组分玻色-爱因斯坦凝聚体(Bose-Einstein condensates,BECs)的量子隧穿特性.从描述三维双组分BECs系统的Gross-Pitaevskii方程(GPE)出发,得到了描述一维体系的GP方程.把体系波函数写成原子数和相位指数的乘积,得到描述体系隧穿特性的费曼方程.数值求解费曼方程,研究了原子之间相互作用(双组分BECs体系原子之间的相互作用包括组分内部原子之间的相互作用和不同组分原子之间的相互作用)对隧穿特性的影响.结果显示,当原子之间的相互作用较弱时,体系发生量子隧穿现象,表现为原子数在平衡位置附近作周期振荡;随着原子之间相互作用增强,体系经历一个临界状态,进入自俘获状态,即由于原子之间相互作用的存在,在对称双势阱中演化的BECs可以呈现出原子数高度的不对称分布,好像绝大数原子被其中一个势阱俘获.从隧穿到自俘获原子之间的相互作用存在一个临界值,从而体系的能量也对应一个临界值,根据体系的哈密顿函数,就能求出相互作用临界值的表达式.     

费米-费米散射长度对费米超流气体在幺正极限区域的隧穿现象影响

运用双势阱模型通过调节费米-费米散射长度研究了超流费米气体在幺正极限区域的隧穿现象. 研究发现费米-费米散射长度对量子隧穿效应有显著的影响. 在确定的区域, 可以得到在双势阱中完全的量子隧穿现象, 而在另一些区域, 这种隧穿就完全消失. 由于在实验室中超流费米气体的散射长度是可以调节的, 所以在实验上可以实现通过调节散射长度来控制超流费米气体的宏观隧穿现象.     

冷原子物理中的一维少体问题

作为构成量子多体系统的基本单元,一维少体系统的研究不仅可以在理论上为多体系统的量子关联及动力学等性质提供更为基本的理解,也可以为实验上制备多体系统提供更加方便和功能更加全面的方法.本文回顾了冷原子物理中一维少体系统最新的实验和理论进展.首先介绍了少体实验中实现的谐振子势阱中确定原子数的精确制备,亚稳态势阱和双阱系统中原子的隧穿,以及强相互作用下等效自旋链的实验结果.然后深度解析了理论研究方面,特别是基于精确可解模型的一些重要结果,包括亚稳态势阱中相互作用原子的隧穿概率,以及相应实验上常见势阱的能谱分析、密度分布、隧穿动力学以及强相互作用极限下的有效自旋链模型等.     

描述大形变核中对力的硬核Bose-Hubbard模型

讨论了一种描述大形变偶偶核邻近轨道对力相互作用近似的硬核Bose-Hubbard模型.利用代数方法得到了该模型对激发谱和相应波函数的严格解.该结果可推广到具有任意自旋和有限格点的硬核Bose-Hubbard和Fermi-Hub-bard模型中去.     

有效质量法调控原子玻色-爱因斯坦凝聚体的双阱动力学

操控原子玻色-爱因斯坦凝聚体在双势阱中的动力学通常是通过改变势阱深度来实现,本文提出了一种基于调节原子有效质量的控制方案,可以在不改变双阱势的前提下操控凝聚体的双阱动力学.利用双模近似,本文解析地导出了超冷原子在双阱势中的隧穿强度和相互作用强度对有效质量的依赖关系,并基于平均场近似数值模拟了在有效质量调节下的凝聚体动力学演化,展示了隧穿振荡和自束缚等典型的双阱动力学行为.此外,本文的研究还发现,借助负有效质量效应,这一方案甚至可以等效地实现对负散射长度原子凝聚体双阱动力学行为的操控.     

双组分玻色-爱因斯坦凝聚体中亚稳态存在条件及其寿命

本文对双势阱中凝聚的冷原子通过约瑟夫森结隧穿时所形成的亚稳态进行研究.通过介观自旋算符建立了体系的精确量子相位模型,利用对量子自旋的势场描述给出了在两阱中振荡的原子之间相位差为时,即亚稳态时所要满足的物理条件,并用瞬子方法计算了该亚稳态存在的寿命.     

三势阱玻色爱因斯坦凝聚体三体复合效应的数值研究

文章中着重研究在三势阱中的凝聚体所受到的非弹性碰撞相互作用,考虑有三体复合耗散和原子填充时三势阱中玻色-爱因斯坦凝聚体动力学性质,研究了三势阱中玻色-爱因斯坦凝聚体系的自囚禁与宏观量子遂穿问题,用数值分析和解析推导的方法,发现自俘获和宏观量子隧穿现,另外,在自俘获和宏观量子隧穿进程中发现了量子拍现象,并对这些现象给出合理的解释。     

对称抛物势阱磁性隧道结中的自旋输运及磁电阻效应

研究了两端具有铁磁接触的对称抛物势阱磁性隧道结(F/SPW/F)中自旋相关的隧穿概率和隧穿磁电阻,讨论了量子尺寸效应和Rashba 自旋轨道耦合作用对自旋极化输运特性的影响.研究结果表明:隧穿概率和隧穿磁电阻随抛物势阱宽度的增加发生周期性的振荡.抛物势阱深度的增加减小了隧穿概率和隧穿磁电阻的振荡频率.Rashba 自旋轨道耦合强度的增加加大了隧穿概率和隧穿磁电阻的振荡频率.隧穿概率和隧穿磁电阻的振幅和峰谷比强烈依赖于两铁磁电极中磁化方向的夹角. 关键词： 磁性隧道结 Rashba 自旋轨道耦合 隧穿概率 隧穿磁电阻     

双势阱中玻色-爱因斯坦凝聚的绝热隧穿

研究了玻色-爱因斯坦凝聚体在双势阱中随着能级差绝热循环变化而发生的绝热隧穿.发现当相互作用较强且初态选择为凝聚体全部置于较浅势阱时,演化过程破坏绝热定理,而演化结果有可能回到初态,也有可能不回到初态,取决于演化周期的选择;另外还发现演化过程表现出对初态选择的依赖,具有不对称的特征.利用能级图和相图,对上述现象给出了解释. 关键词： 玻色-爱因斯坦凝聚 Landau-Zener模型 绝热隧穿     

Two-mode dipolar bosonic junctions

We consider a two-mode atomic Josephson junction realized with dilute dipolar bosons confined by a double-well. We employ the two-site extended Bose-Hubbard Hamiltonian and characterize the ground-state of this system by the Fisher information, coherence visibility, and entanglement entropy. These quantities are studied as functions of the interaction between bosons in different wells. The emergence of Schrödinger’s cat-like state with a loss of coherence is also commented.     

Coupling Effect of Atomic Tunneling States with Local Vibration Modes in Amorphous Materials1

Considering the coupling of the atomic tunneling states with the vibration modes of its nearby atoms, two different kinds of double-well potentials are obtained. At the meantime, the vibration of nearby atoms are softened, and under certain conditions a new double-wel1,potential of higher rank can be induced which makes a hierarchical double-well potential structure possible.     

Nonlinear Landau-Zener tunneling of Bose-Einstein condensate in a spatially magnetic modulated trap

We study tunneling of a Bose-Einstein condensates confined in a effective double-well potential (a single well with a spatially magnetic modulated scattering length, actually), called pseudo double-well trap, in which the interaction of atoms characterized by the s-wave scattering length a _s can be widely tuned with a magnetic-field Feshbach resonance. As a result, corresponding to different nonlinear parameters, the energy levels of the nonlinear Schrödinger equation can have complex structures in their dependence on the bias between the wells. We discuss the emergence of looped levels, which lead to a breakdown of adiabaticity that the Landau-Zener transition probability does not vanish even in the adiabatic limit. Moreover, we also find that the Landau-Zener tunneling in the pseudo trap show many striking properties distinguished from that of the real trap model (where the barrier is created by the external potential). Possible experimental observation in an opticallyinduced photonic lattices in a photorefractive material is suggested.     

A controllable double-well optical trap for cold atoms (or molecules) using a binary <Emphasis Type="Italic">π</Emphasis>-phase plate: experimental demonstration and Monte Carlo simulation

We experimentally demonstrate a practical scheme to form a controllable double-well optical dipole trap for cold atoms (or cold molecules), and give some experimental results as well as the fabrication method of a binary π-phase plate. The dependence of the double-well characteristics on the phase etching error of the π-phase plate and the evolution of the double-well optical trap from two wells to a single one are studied both theoretically and experimentally, and the experimental results are consistent with the theoretical prediction. Furthermore, the dynamic process of loading and splitting of cold ⁸⁷Rb atoms from a standard magneto-optical trap (MOT) into our controllable double-well one are studied by Monte Carlo simulations. Our study shows that the loading efficiency of cold atoms from the standard MOT into our single-well trap can reach 100%, and the relative atomic density will be reduced from 1.0 to ∼0.5 during the evolution of our double-well trap, in which the temperature of cold atoms is reduced from 20 μK to ∼15 μK. In final, some potential applications of our controllable double-well optical trap in atom and molecule optics are briefly discussed.     

Ground States of Ultracold Spin-1 Atoms in a Deep Double-Well Optical Superlattice in a Weak Magnetic Field

The ground states of the ultracold spin-1 atoms trapped in a deep one-dimensional double-well optical superlattice in a weak magnetic field are obtained. It is shown that the ground-state diagrams of the reduced double- well model are remarkably different for the antiferromagnetic and ferromagnetic condensates. The transition between the singlet state and nematic state is observed for the antiferromagnetic interaction atoms, which can be realized by modulating the tunneling parameter or the quadratic Zeeman energy. An experiment to distinguish the different spin states is suggested.     

Interaction of two-level tunneling system with phonons

Properties of two-level tunneling system which interacts with lattice vibrations are discussed in the framework of the polaron theory and the phase space approach. The decrease of the dynamic distortion of the lattice with increasing ratio η of the rigid-lattice tunneling matrix element to the small polaron binding energy is calculated in the intermediate coupling regime 0 < η < 2. A relatively sharp transition from the distorted to the undistorted state of the lattice takes place when η crosses the value 2. The expressions for the renormalized tunneling matrix element and for the longitudinal relaxation time T₁ are derived. A two-level tunneling model in which the double-well potential is asymmetric is also investigated.     

Tunneling and Self-Trapping of Superfluid Fermi Gases in BCS-BEC Crossover

We investigate tunneling and self-trapping of superfluid Fermi gases under a two-mode ansatz in different regimes of the crossover from Bardeen-Cooper-Schrieffer (BCS) superfluid to Bose-Einstein condensates (BEC). Starting from a generalized equation of state, we derive the coupled equations of relative atom-pair number and relative phase about superfluid Fermi gases in a double-well system and then classify the different oscillation behaviors by the
tunneling strength and interactions between atoms. Tunneling and self-trapping behaviors are considered in the whole BCS-BEC crossover in the case of a symmetric double-well potential. We show that the nonlinear interaction between atoms makes the self-trapping more easily realized in BCS regime than in the BEC regime and stability analysis is also given.     

量子遂穿在双阱异核分子形成过程中的作用(英文）

对于束缚在双阱中的两组分玻色－爱因斯坦凝聚体,本文研究了基于光缔合机制形成分子的过程中,量子隧穿所起的作用．该双阱外势可以在实验上利用磁场生成的谐振子势和由蓝失谐光或射频源生成的中心势垒来实现．在合适的光场中,我们分析了系统在不同初始状态下的短时极限量子动力学,同时对系统做了在平均场近似下的数值计算分析．我们发现无论是隧穿强度还是初始状态的制备都对系统的动力学有很大的影响．我们还计算了同核分子在这些情况下的结果,并和异核分子计算的结果作了比较．量子化的光缔合光场在分子形成过程的影响也在文章中给予了讨论．     

The effect of an external electric field on the optical properties of a quantum molecule with a resonance D(-)-state

The average binding energy and the level width for the resonant D^(-)-state in a quantum molecule have been calculated in the presence of an external electric field. The calculations were performed in the zeroradius potential model with allowance for the tunneling decay of the resonant state. The external electric field is shown to stimulate the decay of resonant D^(-)-states under conditions of dissipative tunneling. It was found that the curve of the probability of photoionization of the D^(-)-center as a function of the external electric field strength has two peaks that are connected with a change in the symmetry of the double-well oscillator potential of the quantum molecule and with the transformation (caused by the electric field) of envelope wave functions, respectively.