用电子束任意雕琢原子团打开冷原子物理的新天地

近十年来,物理学家们非常巧妙地运用光格(呈有序排列的光阱)和超冷原子构成的量子"模型"对诸如超导现象等固体性质进行模拟研究.然而,人们一直没有找到一种很好的方法将光格中特定位置的原子去掉,这就使光格一超冷原子量子模型的应用范围受到较大的限制.如果可以对光格中的每个超冷原子进行针对性操作,那么光格一超冷原子量子模型将可以模拟更多种类的固体材料.     

第六届冷原子物理国际学术研讨会(ISCAP-Ⅵ)第一轮通知

<正>第六届冷原子物理国际学术研讨会(ISCAP-Ⅵ)将于2014年6月14-17日在山西太原举行。该系列研讨会自2004年创办以来,每偶数年举办一次,已分别于2004年(庐山,ISCAP-Ⅰ)、2006年(千岛湖、ISCAP-Ⅱ)、2008年(武汉,ISCAP-Ⅲ)、2010年(舟山,ISCAP-Ⅳ)和2012年(宜昌,ISCAP-Ⅴ)举办了五届。该系列会议由中国物理学会原子分子物理专业委员会、中国科学院、国家自然科学基金     

两体问题的质心速度与一维完全弹性碰撞

将两体问题的质心速度公式应用于一维完全弹性碰撞问题，从而导出一系列有用的结果，既可丰富两体问题的有关内容，又为讨论一维完全弹性碰撞问题，简化其计算提供新的方法。     

对称性对四体系统结构和内部运动的影响

文中用谐振子乘积基展开法求解了四体系统的Schrdinger方程.通过分析波函数及形状密度函数在多维坐标空间的分布,比较了四体全对称0⁺态,四体金对称0^－态和四体全反对称0⁺态,四体全反对称0^－态的结构和内部运动的差异;讨论了对称性的影响.     

核少体问题研究进展简况

本文概要介绍了近几年来国防上关于核少体问题研究方面的进展状况及新动向． The current status and progress are outlined in few-body nuclear physics research. Latest trends in this field are reviewed as well.     

制冷剂气体水合物用于蓄冷空调中的探讨

由于能源和电力供应紧张,蓄冷技术引起关注。文中从节能环保的角度,分析了制冷剂气体水合物用于蓄冷空调的必要性和优越性。概括阐述了制冷剂气体水合物的工质选择及替代、促晶技术和蓄冷系统方面的研究,为气体水合物尽快实用化提出研究重点。     

核结构模型中的两体以上相互作用（英文）

讨论了核结构模型中两体以上相互作用的可能形式。首先以基于手征微扰论并适于描述轻核的三体接触型相互作用为例,讨论了能合理描述3H 和3He 结合能的三核子接触型相互作用相关的两个低能有效耦合参数c_D 和c_E间的关系并通过4He 结合能给出了相应的物理参数区。其次通过Okubo-Lee-Suzuzki 有效相互作用方法对核多体问题在有限模型空间的求解,论证了A-体相互作用项。最后利用包含了A-体推广对力的可解模型对重核的同位素长链进行了分析。以132Sn 为核芯,通过对Sn 同位素链的计算揭示了推广对力参数G（A） 与模型价核子空间维数dim（A） 间的显著关系:G（A）=259.436 dim（A）-0.9985。这些分析结果说明,有必要对核中经手征微扰论或其它唯象理论所得到的NNN-,NNNN-,及A-体相互作用作进一步的研究。We discuss modeling of nuclear structure beyond the 2-body interaction paradigm. Our first example is related to the need of three nucleon contact interaction terms suggested by chiral perturbation theory. The relationship of the two low-energy effective coupling parameters for the relevant three nucleon contact interaction terms c_D and c_E that reproduce the binding energy of 3H and 3He has been emphasized and the physically relevant parameter region has been ilustrated using the binding energy of 4He. Further justification of A-body interaction terms is outlined based on the Okubo-Lee-Suzuki effective interaction method used in solving the nuclear many-body problem within a finite model space. The third example we use is an exactly solvable A-body extended paring interaction applied to heavy nuclei with a long isotopic chain; in particular using 132Sn as closed core system illustrates a remarkable relationship between the extended pairing strength G(A) and the size of the valence space dim(A) for the members of the Sn-isotope chain: G(A)=αdim(A)-β with α=259.436 and β =0.9985 which is actually a one parameter expression since β is practically 1. These three cases present evidence for the need of better understanding of the NNN-, NNNN-, and A-body interactions in nuclei either derived from ChPT or from a phenomenological considerations.     

利用少体方法计算_Λ~3H,_Λ~4H,_Λ~4He的基态结合能

在手征SU（3）夸克模型和谐振子基下,Y-N（超子-核子）相互作用采用非定域势,N-N相互作用采用高斯型势,根据少体理论研究并计算了轻超核3 H 4 H 4He,,ΛΛΛ的基态结合能,并同实验值做了比较。     

精确几何单元下弹性薄体结构问题的边界元法分析

对圆弧单元下的几乎奇异积分,采用变量替换法进行正则化,然后采用通常的高斯求积公式进行计算,可获得相当高的计算精度,即使是超薄的薄体结构,方法仍然十分有效.     

GPS掩星一维弯曲角算子在四维变分资料同化系统中的实现方法研究

GPS无线电掩星资料的良好特性使其作为十分重要的观测资料在欧洲 及美国数值天气预报中效果明显. 本文设计了一维弯曲角算子在四维变分资料同化系统中的实现方法和质量控制策略. 详细阐述了一维弯曲角正演算子及其切线性/伴随算子在全球四维变分资料同化系统中的实现步骤和过程, 其中折射率计算中采用Rüeger的折射率最佳平均因子的三项表达式, 计算出更加精确的折射率值. 对2012年8月份的GPS无线电掩星资料进行了观测误差统计, 引入了更加符合四维变分资料同化系统实际情况的一维弯曲角观测误差模型和质量控制策略. 同时, 对比了观测误差统计试验中同化GPS无线电掩星资料的模式背景场和未同化GPS无线电掩星资料的背景场的观测误差统计结果, 发现同化GPS无线电掩星资料之后的观测误差统计结果在全球区域正作用十分明显, 尤其是在中低纬度地区, 高度在10 km 以上的区域观测误差减小十分明显. 关键词： GPS无线电掩星 一维弯曲角算子 四维变分同化系统 质量控制     

Three ultracold fermions in a two-dimensional anisotropic harmonic confinement

We calculate the energy spectrum of three identical fermionic ultracold atoms in two different internal states confined in a two-dimensional anisotropic harmonic trap. Using the solutions of the corresponding two-body problems obtained in our previous work (Chen et al 2020 Phys. Rev. A 101, 053624), we derive the explicit transcendental equation for the eigen-energies, from which the energy spectrum is derived. Our results can be used for the calculation of the 3rd Virial coefficients or the studies of few-body dynamics.     

Quantum dynamics in ultracold atomic physics

We review recent developments in the theory of quantum dynamics in ultracold atomic physics, including exact techniques and methods based on phase-space mappings that are applicable when the complexity becomes exponentially large. Phase-space representations include the truncated Wigner, positive-P and general Gaussian operator representations which can treat both bosons and fermions. These phase-space methods include both traditional approaches using a phase-space of classical dimension, and more recent methods that use a non-classical phase-space of increased dimensionality. Examples used include quantum Einstein-Podolsky-Rosen (EPR) entanglement of a four-mode BEC, time-reversal tests of dephasing in single-mode traps, BEC quantum collisions with up to 106 modes and 105 interacting particles, quantum interferometry in a multi-mode trap with nonlinear absorption, and the theory of quantum entropy in phase-space. We also treat the approach of variational optimization of the sampling error, giving an elementary example of a nonlinear oscillator.     

Quantum simulation of quantum many-body systems with ultracold two-electron atoms in an optical lattice

Ultracold atoms in an optical lattice provide a unique approach to study quantum many-body systems, previously only possible by using condensed-matter experimental systems. This new approach, often called quantum simulation, becomes possible because of the high controllability of the system parameters and the inherent cleanness without lattice defects and impurities. In this article, we review recent developments in this rapidly growing field of ultracold atoms in an optical lattice, with special focus on quantum simulations using our newly created quantum many-body system of two-electron atoms of ytterbium. In addition, we also mention other interesting possibilities offered by this novel experimental platform, such as applications to precision measurements for studying fundamental physics and a Rydberg atom quantum computation.     

Scattering amplitude and two-body loss of ultracold alkaline-earth atoms in a shaking synthetic magnetic field

The idea of manipulating the interaction between ultracold fermionic alkaline-earth (like) atoms via a laser-induced periodical synthetic magnetic field was proposed in Kanász-Nagy et al (2018 Phys. Rev. B 97, 155156). In that work, it was shown that in the presence of the shaking synthetic magnetic field, two atoms in ¹S₀ and ³P₀ states experience a periodical interaction in a rotated frame, and the effective inter-atomic interaction was approximated as the time-averaged operator of this time-dependent interaction. This technique is supposed to be efficient for ¹⁷³Yb atoms which have a large natural scattering length. Here we examine this time-averaging approximation and derive the rate of the two-body loss induced by the shaking of the synthetic magnetic field, by calculating the zero-energy inter-atomic scattering amplitude corresponding to the explicit periodical interaction. We find that for the typical cases with shaking angular frequency λ of the synthetic magnetic field being of the order of (2π) kHz, the time-averaging approximation is applicable only when the shaking amplitude is small enough. Moreover, the two-body loss rate increases with the shaking amplitude, and is of the order of 10⁻¹⁰ cm³ · s⁻¹ or even larger when the time-averaging approximation is not applicable. Our results are helpful for the quantum simulations with ultracold gases of fermionic alkaline-earth (like) atoms.     

Exact solution to a class of generalized Kitaev spin-1/2 models in arbitrary dimensions

We construct a class of exactly solvable generalized Kitaev spin-1/2 models in arbitrary dimensions, which is beyond the category of quantum compass models. The Jordan-Wigner transformation is employed to prove the exact solvability. An exactly solvable quantum spin-1/2 model can be mapped to a gas of free Majorana fermions coupled to static Z2 gauge fields. We classify these exactly solvable models according to their parent models. Any model belonging to this class can be generated by one of the parent models. For illustration, a two dimensional(2D) tetragon-octagon model and a three dimensional(3D) xy bond model are studied.     

Effects of electron correlation on superconductivity in the Hatsugai–Kohmoto model

Understanding how electrons form pairs in the presence of strong electron correlations demands going beyond the BCS paradigm. We study a correlated superconducting model where the correlation effects are accounted for by a U term local in momentum space. The electron correlation is treated exactly while the electron pairing is treated approximately using the mean-field theory. The self-consistent equation for the pair potential is derived and solved. Somewhat contrary to expectation, a weak attractive U comparable to the pair potential can destroy the superconductivity, whereas for weak to intermediate repulsive U, the pair potential can be enhanced. The fidelity of the mean-field ground state is calculated to describe the strength of the elelectron correlation. We show that the pair potential is not equal to the single-electron superconducting gap for the strongly correlated superconductors, in contrast to the uncorrelated BCS limit.     

Stark spectra of Rydberg states in atomic cesium in the vicinity of n=18

The Stark structures in a cesium atom around n=18 are numerically calculated. The results show that the components of 20D states with a small azimuthal quantum number |m| shift upward a lot, and those with a large |m| shift downward a little within 1100 V/cm. All components of P states shift downward. Experimental work has been performed in ultracold atomic cesium. Atoms initially in 6P3/2 state are excited to high-n Rydberg states by a polarization light perpendicular to the field, and Stark spectra with |m|=1/2,3/2,5/2 are simultaneously observed with a large linewidth for the first time. The observed spectra are analyzed in detail. The relative transition probability is calculated. The experimental results are in good agreement with our numerical computation.     

关于数学物理方法课程的若干问答(续2)

26如果偏微分方程具有一定的对称性(不变性),它的解是否一定具有同样的对称性(不变性)?不一定!例如,二维拉普拉斯方程具有平移不变性、反射不变性以及旋转不变性,但是它的解x或y就不具有这些不变性.同样,x2-y2也是二维拉普拉斯方程的解,但是它也不具有平移不变性和旋转     

Large-Distance Behavior of Particle Correlations in the Two-Dimensional Two-Component Plasma

The model under consideration is a two-dimensional two-component plasma, i.e., a continuous system of two species of pointlike particles of opposite charges ±1, interacting through the logarithmic Coulomb interaction. Using the exact results for the form-factors of an equivalent Euclidean sine-Gordon theory, we derive the large-distance behavior of the pair correlation functions between charged particles. This asymptotic behavior is checked on a few lower orders of its -expansion ( is the inverse temperature) around the Debye–Hückel limit 0, and at the free-fermion point =2 at which the collapse of positive-negative pairs of charges occurs.     

Low—Lying States of the A^＋B^—A^＋B^— Coulomb systems in Two—Dimensional Quantum Dots

The features of the low-lying spectra of four-body A B-A B- systems have been dedudced based on symmetry,Using the method of few-body physics,we calculate the energy spectra of A B-A B- systems in a harmonic quantum dot.We find tha t the biexcition in a two-dimensional quantum dot may have other bound excited states and the quantum mechanical symmetry plays a crucial role in determining the energy levels and structures of the low-lying the quantum mechanical symmetry plays a crucial role in determining the energy levels and structures of the low-lying states.