三模激光驱动光晶格中玻色-爱因斯坦凝聚体的精确Floquet态

利用平均场理论研究了一维的三模激光驱动光晶格中三组分玻色-爱因斯坦凝聚体(Bose-Einstein condensates,BECs)的精确非定态解.从描述一维的三组分BECs系统的耦合Gross-Pitaevskii(GP)方程出发,利用原子间的平均场相互作用与外势之间的平衡条件,引入三个等效的相互作用系数,得到了一组等价的非耦合GP方程.结果表明,对于合适的参数区域,体系存在一种随时间和空间都呈周期性变化的Floquet态.分析和讨论了各组分BECs的粒子数密度、相位、粒子流速度以及粒子流密度的时间演化特性.     

凝聚体隙孤子的动力控制

发展了研究光晶格中波色-爱因斯坦凝聚体线性与非线性激发动力学性质的系统控制方法,得到了周期势下波色-爱因斯坦凝聚体孤子解析解和典型色散关系.通过对孤子解析解的分析,发现原子相互作用强度对波色-爱因斯坦凝聚体孤子的动力学性质有重要影响.     

一维倾斜光晶格势阱中两组分玻色-爱因斯坦凝聚体的矢量孤子解及其稳定性

用变分方法研究了在一维倾斜光晶格势阱中的两组分玻色-爱因斯坦凝聚体,分别得到了对称不分离、对称分离和不对称不分离三种不同类型的矢量孤子,并与数值模拟得到的结果进行比较,两者吻合得很好。进一步通过引入强扰动,研究了凝聚体中孤子的稳定性问题。     

Floquet相空间方法分析周期驱动下原子玻色爱因斯坦凝聚体动力学

用相空间动力学方法研究一维无限深势阱内的原子玻色爱因斯坦凝聚体受到时域周期性微扰时的动力学行为.通过功角变换和共振频率近似，在Floquet相空间中构造有效的势场来预言玻色爱因斯坦凝聚体的运动，并通过数值模拟实空间动力学方程，验证了该方法.     

囚禁势中玻色-爱因斯坦凝聚体的半轴宽度和粒子数密度

文章计算了准一维、准二维、球对称、轴对称系统的玻色-爱因斯坦凝聚体的半轴宽度和粒子数密度,采用求基态能量极小值和令势能等于相互作用能的办法,讨论的问题包括凝聚体半轴宽度的解析表达式、粒子数密度的理论计算值与实验数据的对比分析和吸引相互作用系统的塌缩粒子数。     

一维无限深势阱调制下的空间光孤子

运用一种发展了的分离变量法求解在外势调制下的（2＋1）维变系数非线性薛定谔方程，得到了精确的孤子解。研究表明空间光孤子在一维无限深势阱型势调制下呈现出新的空间分布和演化特性。     

费曼传播子方法研究超流费米原子气体从一维光晶格中释放后的相干演化

文章基于描述零温超流费米气体的序参量方程，通过费曼传播子方法，解析了关闭光晶格和谐振子势后，超流费米原子气体的相干演化，以及仅关闭光晶格，费米超流在谐振子势中的周期演化。     

反抛物势与双光晶格势中的三维玻色-爱因斯坦凝聚涡旋孤子

提出了一种处理囚禁于反抛物势和双光晶格复合势中玻色-爱因斯坦凝聚涡旋孤子动力学的能量密度泛函和直接数值仿真相结合的方法.利用静态Gross-Pitaevskii方程和柱对称玻色-爱因斯坦凝聚涡旋孤子试探波函数,给出了玻色-爱因斯坦凝聚静态涡旋孤子能量密度泛函的解析式,再运用数值模拟含时Gross-Pi-taevskii方程的方法,得到了稳定演化的涡旋孤子;并且通过调控双光晶格势,实现了玻色-爱因斯坦凝聚涡旋孤子从某一晶格势槽为初始位置到任意位置的操控,为玻色-爱因斯坦凝聚的实验和应用研究提供了一定的理论依据.值得指出的是,双涡旋孤子的稳定演化与操控是最重要的发现.     

光晶格中偶极BEC的调制不稳定性

在GP方程和离散Schr d inger方程的基础上,对光晶格中偶极玻色-爱因斯坦凝聚体(BEC)的调制不稳定性进行了研究,得到了光晶格偶极BEC原子系统的激发谱和调制不稳定性区域与在位相互作用以及偶极-偶极相互作用之间的关系.结果显示,偶极-偶极相互作用对光晶格中偶极BEC的非线性激发和稳定性有很大的影响,为实际应用中如何操控偶极BEC提供有用的信息.     

一维光晶格中排斥费米气体的超流特性

用密度矩阵重整化群方法（DMRG）研究了自旋轨道耦合与谐振外势同时存在时的一维光晶格的排斥费米原子气体的基态性质。研究发现,在一维光晶格中的占据数小于半填充情况下,当只考虑谐振外势时,系统的排斥相互作用超过某一临界值时,系统存在费米超流。当同时考虑谐振外势和自旋轨道耦合时,发现当系统处于金属态时,自旋轨道耦合增强了金属性;当系统处于Mott绝缘态时,自旋轨道耦合减弱了绝缘性且存在超流性。最后分析了在自旋轨道耦合作用下系统的填充数对配对的影响,谐振外势强度的变化与自旋轨道耦合对束缚态的影响。     

囚禁在光格中的波色-爱因斯坦凝聚体孤子

利用数值模拟解Gross-Pitaevskii方程来研究囚禁在光格中的波色-爱因斯坦凝聚体明孤子，发现周期性光格可被用作为可控的物质波分裂器，其分裂效果与孤子在光格中的初始位置、势阱中的原子数、以及光格电势的幅度、波矢有关。     

非对称囚禁二维玻色-爱因斯坦凝聚孤子的演化

利用变分法解G ross-P itaevsk ii方程,研究了囚禁在各向异性势阱中的二维饼状玻色-爱因斯坦凝聚体(BEC)孤子的演化规律,发现通过在圆柱形对称的磁阱中的某一方向引入光格电势,不仅使BEC孤子在该方向趋向稳定,而且通过相互耦合作用也能影响其它方向从而使孤子的膨胀变慢,使BEC孤子的稳定性增加。其效果与势阱中的原子数、势阱系数和光格参数有关。     

Formation and propagation of matter-wave soliton trains

Attraction between the atoms of a Bose-Einstein condensate renders it unstable to collapse, although a condensate with a limited number of atoms can be stabilized by confinement in an atom trap. However, beyond this number the condensate collapses. Condensates constrained to one-dimensional motion with attractive interactions are predicted to form stable solitons, in which the attractive forces exactly compensate for wave-packet dispersion. Here we report the formation of bright solitons of (7)Li atoms in a quasi-one-dimensional optical trap, by magnetically tuning the interactions in a stable Bose-Einstein condensate from repulsive to attractive. The solitons are set in motion by offsetting the optical potential, and are observed to propagate in the potential for many oscillatory cycles without spreading. We observe a soliton train, containing many solitons; repulsive interactions between neighbouring solitons are inferred from their motion.     

Observation of two-dimensional discrete solitons in optically induced nonlinear photonic lattices

Nonlinear periodic lattices occur in a large variety of systems, such as biological molecules, nonlinear optical waveguides, solid-state systems and Bose-Einstein condensates. The underlying dynamics in these systems is dominated by the interplay between tunnelling between adjacent potential wells and nonlinearity. A balance between these two effects can result in a self-localized state: a lattice or 'discrete' soliton. Direct observation of lattice solitons has so far been limited to one-dimensional systems, namely in arrays of nonlinear optical waveguides. However, many fundamental features are expected to occur in higher dimensions, such as vortex lattice solitons, bright lattice solitons that carry angular momentum, and three-dimensional collisions between lattice solitons. Here, we report the experimental observation of two-dimensional (2D) lattice solitons. We use optical induction, the interference of two or more plane waves in a photosensitive material, to create a 2D photonic lattice in which the solitons form. Our results pave the way for the realization of a variety of nonlinear localization phenomena in photonic lattices and crystals. Finally, our observation directly relates to the proposed lattice solitons in Bose-Einstein condensates, which can be observed in optically induced periodic potentials.     

Bose-Einstein condensation of quasi-equilibrium magnons at room temperature under pumping

Bose-Einstein condensation is one of the most fascinating phenomena predicted by quantum mechanics. It involves the formation of a collective quantum state composed of identical particles with integer angular momentum (bosons), if the particle density exceeds a critical value. To achieve Bose-Einstein condensation, one can either decrease the temperature or increase the density of bosons. It has been predicted that a quasi-equilibrium system of bosons could undergo Bose-Einstein condensation even at relatively high temperatures, if the flow rate of energy pumped into the system exceeds a critical value. Here we report the observation of Bose-Einstein condensation in a gas of magnons at room temperature. Magnons are the quanta of magnetic excitations in a magnetically ordered ensemble of magnetic moments. In thermal equilibrium, they can be described by Bose-Einstein statistics with zero chemical potential and a temperature-dependent density. In the experiments presented here, we show that by using a technique of microwave pumping it is possible to excite additional magnons and to create a gas of quasi-equilibrium magnons with a non-zero chemical potential. With increasing pumping intensity, the chemical potential reaches the energy of the lowest magnon state, and a Bose condensate of magnons is formed.     

Towards Bose-Einstein condensation of excitons in potential traps

An exciton is an electron-hole bound pair in a semiconductor. In the low-density limit, it is a composite Bose quasi-particle, akin to the hydrogen atom. Just as in dilute atomic gases, reducing the temperature or increasing the exciton density increases the occupation numbers of the low-energy states leading to quantum degeneracy and eventually to Bose-Einstein condensation (BEC). Because the exciton mass is small--even smaller than the free electron mass--exciton BEC should occur at temperatures of about 1 K, many orders of magnitude higher than for atoms. However, it is in practice difficult to reach BEC conditions, as the temperature of excitons can considerably exceed that of the semiconductor lattice. The search for exciton BEC has concentrated on long-lived excitons: the exciton lifetime against electron-hole recombination therefore should exceed the characteristic timescale for the cooling of initially hot photo-generated excitons. Until now, all experiments on atom condensation were performed on atomic gases confined in the potential traps. Inspired by these experiments, and using specially designed semiconductor nanostructures, we have collected quasi-two-dimensional excitons in an in-plane potential trap. Our photoluminescence measurements show that the quasi-two-dimensional excitons indeed condense at the bottom of the traps, giving rise to a statistically degenerate Bose gas.     

二维囚禁广义玻色气体的玻色-爱因斯坦凝聚

应用广义玻色-爱因斯坦分布函数研究在幂函数外势中二维广义玻色气体的玻色-爱因斯坦凝聚(BEC),导出二维广义玻色气体的临界温度、基态粒子占据率和热容量等物理量的解析表达式,讨论了非广延参数q对玻色系统热统计性质的影响.