Xe-NH (X3∑-)体系的势能面和冷碰撞动力学研究

以超冷Xe原子感应冷却NH（X³∑^-）分子实验为背景,理论研究磁场中Xe和NH的冷碰撞动力学性质.通过从头算方法得到了解析表达的Xe-NH体系势能面,并在此基础上采用量子动力学计算方法,研究了磁场条件下NH低场追索态（n=0,m_j=1）的冷碰撞塞曼弛豫截面.结果表明超冷Xe原子感应冷却NH分子可能在实验上难以实施.     

Calculation of the beta decay of Pd. Quasiparticle random phase approximation results

Single beta decay transitions in ^114–120Pd are calculated. Theoreticalβ⁺ and β⁻ strength distributions, for transitions to 1⁺ states in the nuclei ^114–120Ag and ^114–120Rh, are obtained in the framework of the quasiparticle random phase approximation (QRPA). The effective two-body interaction which is used in the calculations is constructed from the Bonn one-boson-exchange potential (OBEP). Particle-hole and particle-particle like channels of the two-body force are included in the definition of the QRPA matrix equations. Effects associated with the particle number violation of the quasiparticle mean field are accounted for by using a particle-number-projected version of the QRPA formalism. Theoretical strength distributions for the β⁻ and β⁺ braches are shown and compared with data.     

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.     

Condensation of Fermions in the double-well potential

The density distribution of ultracold two-component fermionic gases 6Li, which are confined in a gradient magnetic field and a symmetrical double-well potential, is investigated by employing local-density approximation. It is found that three different regimes including quasi-molecular Bose-Einstein condensation （BECm）, the dimers in the unitarity limit （ULd）, and Bardeen-Cooper-Schrieffer superfluid （BCS） can coexist at the same time. Furthermore, the ranges of these regimes can be controlled to some extent by tuning the gradient of the magnetic field and the parameters characterizing the properties of the double-well potential. This study is of guidance and significance for experimentally realizing the coexistence of BECm, ULd, and BCS in the double-well potential.     

Optical pumping of the 2p3sP0 State of Ne (I = 3/2): g factor and metastability exchange cross section

A C.W. multi-mode dye laser is used to obtain by optical pumping an orientation of the 2p⁵ 3s³P₀ (F = 3/2) state of ²¹Ne. A magnetic resonance experiment leads to the measurement of the g factor g (³P₀) = 3.027 (8) × 10⁻⁴ to be compared with the theoretical prediction (3.025(6) × 10⁻⁴). One obtains also the metastability exchange cross section σ(³P₀) = 18.4 ± 4 Ų for collisions between metastable (³P₀) Ne atoms and ground state Ne atoms. This result is compared with other measurements and theoretical evaluation.     

用B-splines技术计算超强平行外磁场中氢分子离子的能级

考虑两核之间的相互作用,采用单中心展开方法和B-splines技术构建氢分子离子的径向和角向波函数,计算超强平行外磁场中氢分子离子的能级E_b(m=0,-1,-2,-3,-4,-5)和两核间的平衡距离2R.计算中,磁场强度从2.35×10⁶T变到2.35×10⁸T.对比绝热变分近似计算结果,计算精度提高的范围在0.00015 Ry~0.0488 Ry之间;对比变分近似计算结果,计算精度提高的范围在0.0029 Ry~0.0257 Ry之间.这些计算结果表明,用二重B-splines基函数展开方法使氢分子离子的波函数的完备性更好,并能得到比绝热变分近似和绝热近似方法更高的计算精度.     

Calculation of Excited States of He Atoms in a Strong Magnetic Field

A recently developed B-spline algorithm is extended and utilized to calculate excited states of He atoms in the presence of strong magnetic fields. Binding energies are presented for He in the five excited atomic states 2¹0⁺, 1¹0^-, 2¹0^-, 1¹(-1)⁺, and 2¹(-1)⁺ with magnetic field strength ranging from 0.0001 to 10 a.u. The obtained energies are compared with available theoretical data, and found to be in good agreement. We investigate influence of magnetic fields on atomic structures of multielectron atoms, and illustrate that how electron probability density distributions change with increasing magnetic field strength. The current approach is directly applicable to simulations of discrete spectra for He atoms in the atmospheres of magnetized white dwarf stars.     

Condensation of pairs of fermionic atoms near a Feshbach resonance

We have observed Bose-Einstein condensation of pairs of fermionic atoms in an ultracold 6Li gas at magnetic fields above a Feshbach resonance, where no stable 6Li2 molecules would exist in vacuum. We accurately determined the position of the resonance to be 822+/-3 G. Molecular Bose-Einstein condensates were detected after a fast magnetic field ramp, which transferred pairs of atoms at close distances into bound molecules. Condensate fractions as high as 80% were obtained. The large condensate fractions are interpreted in terms of preexisting molecules which are quasistable even above the two-body Feshbach resonance due to the presence of the degenerate Fermi gas.     

轨道Feshbach共振附近类碱土金属原子的杂质态问题

近年来,碱土金属原子和类碱土金属原子体系的研究成为冷原子物理的研究热点之一.特别是最近在~(173)Yb原子中发现的轨道Feshbach共振,使得研究有强相互作用的碱土金属和类碱土金属原子系统成为可能,极大扩展了此类原子体系的研究范围.本文介绍了~(173)Yb费米气体在轨道Feshbach共振附近的杂质态问题.在此问题中,位于~3P0态的杂质原子与处于基态的背景费米海相互作用,并在费米海表面产生分子态或极化子态.本文使用试探波函数的研究方法,首先对分子态和吸引极化子态进行介绍,并重点描述了分子态与吸引极化子态间的转变.其次归纳总结了排斥极化子态的相关性质,如有效质量、衰变率等.然后考虑双费米面情况,介绍在闭通道中引入另外一个费米面对系统产生的影响.最后简要介绍二维~(173)Yb费米气体中的杂质态问题.     

Density and spin response functions in ultracold fermionic atom gases

We propose a new method of detecting the onset of superfluidity in a two-component ultracold fermionic gas of atoms governed by an attractive short-range interaction. By studying the two-body correlation functions we find that a measurement of the momentum distribution of the density and spin-response functions allows one to access separately the normal and anomalous densities. The change in sign at low momentum transfer of the normal-ordered part of the density response function signals the transition between a BEC and a BCS regime, characterized by small and large pairs, respectively. This change in sign of the density response function represents an unambiguous signature of the BEC-to-BCS crossover. Spin rotational symmetry breaking due to the magnetic field, if observed, can be used to validate the one-channel model.     

复合外场中磁光材料(BiTm)3(FeGa)5O12薄膜畴壁运动特性的研究

通过对BiTm)₃(FeGa)₅O₁₂膜施工加低频交变磁场,匀速率增加的直流磁场和同时对该膜施加这两种磁场(复合外场),用照相划线读数方法和通过电荷耦合器件(CCD)-计算机作数字化处理获得磁畴壁(DW)的相对百分数。结果表明:(1)复合外场下DW运动规律中存在交互作用项;(2)低频交变磁场幅值(140A/m)远低于等效阻力场(10³A/m)时,DW可以运动,但不同步,频率大于1Hz时明显滞后,(3)利用图像转换有利于提高实验结果的分辨率。     

The axial isoscalar neutral current from inelastic electron-nuclear scattering

Parity violating effects due to neutral currents in isoscalar 0⁺→1⁺ nuclear transitions induced by electron scattering are enhanced owing to the small isoscalar magnetic dipole strength. A polarization asymmetry of the order 10⁻⁴ is expected at q 100 MeV for the ¹²C transition to the 1⁺(T = 0) state at 12.71 MeV. It would allow to single out the (electron vector current) × (hardonic axial isoscalar current) quantum numbers and couplings of the neutral current interaction.     

Universal properties of self-avoiding walks from two-dimensional field theory

We use the recently conjectured exact S-matrix of the massive O(n) model to derive its form factors and ground state energy. This information is then used in the limit n → 0 to obtain quantitative results for various universal properties of self-avoiding chains and loops. In particular, we give the first theoretical prediction of the amplitude ratio C/D which relates the mean square end-to-end distance of chains to the mean square radius of gyration of closed loops. This agrees with the results from lattice enumeration studies to within their errors, and gives strong support for the various assumptions which enter into the field theoretic derivation. In addition, we obtain results for the scaling function of the structure factor of long loops, and for various amplitude ratios measuring the shape of self-avoiding chains. These quantities are all related to moments of correlation functions which are evaluated as a sum over m-particle intermediate states in the corresponding field theory. We show that in almost all cases, the restriction to m 2 gives results which are accurate to at least one part in 10³. This remarkable fact is traced to a softening of the m > 2 branch cuts relative to their behaviour based on phase space arguments alone, a result which follows from the threshold behaviour of the two-body S-matrix, S(O) = −1. Since this is a general property of interacting 2D field theories, it suggests that similar approximation may well hold for other models. However, we also study the moments of the area of self-avoiding loops, and show that, in this case, the two-particle approximation is not valid.     

Production of dual species Bose–Einstein condensates of ~(39)K and ~(87)Rb

We report the production of~(39) K and~(87) Rb Bose–Einstein condensates(BECs) in the lowest hyperfine states |F =1, m_F = 1 simultaneously. We collect atoms in bright/dark magneto-optical traps(MOTs) of~(39) K/~(87) Rb to overcome the light-assisted losses of~(39) K atoms. Gray molasses cooling on the D1 line of the~(39) K is used to effectively increase the phase density, which improves the loading efficiency of~(39) K into the quadrupole magnetic trap. Simultaneously, the normal molasses is employed for~(87) Rb. After the microwave evaporation cooling on~(87) Rb in the optically plugged magnetic trap,the atoms mixture is transferred to a crossed optical dipole trap, where the collisional properties of the two species in different combinations of the hyperfine states are studied. The dual species BECs of~(39) K and~(87) Rb are obtained by further evaporative cooling in an optical dipole trap at a magnetic field of 372.6 G with the background repulsive interspecies scattering length a_(KRb)= 34 a_0(a_0 is the Bohr radius) and the intraspecies scattering length a_K= 20.05 a_0.     

π-electroproduction on hydrogen near threshold at four-momentum transfers of 0.2, 0.4 and 0.6 GeV

The reaction e + p → e + π⁰ + p was measured near the one pion threshold, detecting the final electron and proton in coincidence for values of q² = 0.2, 0.4 and 0.6 GeV². The slope of the cross section at threshold is determined. The data are compared with those of the e + p → e + π⁺ + n reaction, measured simultaneously, and with the results of pseudovector Born approximation and with dispersion theoretical calculations.     

Meissner screening by induced weak charge in the dense Weinberg-Salam system

The magnetic screening in cold electroweak matter at high density of leptons J_LM_W³/6π² is investigated within the approximation known to guarantee the Bose-Einstein condensation of W^±-mesons. It is shown that the photon in this medium acquires a magnetic mass, the electro-magnetic field becoming short-range. It is found that the Meissner damping of a magnetic field is provided in this approximation first of all by an induced polarization charge of weak nature.     

超冷温度下钾和铯原子间弹性散射特性的精确计算

本文分别用量子方法和半经典方法计算了超冷钾和铯原子之间弹性碰撞的s波散射长度,有效力程和p波散射长度等散射参数. 超冷温度下³⁹K-¹³³Cs原子间的弹性散射截面主要为s波贡献,随着碰撞能量的增加散射截面有丰富的形状共振出现, 计算发现单重态和三重态截面分别存在显著的g波和d波形状共振.另外,本文应用简并内态近似方法获得了⁴¹K-¹³³Cs 超精细态相互作用时的s波散射长度.     

激光照射中Z薄靶等离子体状态的计算-激光等离子体相互作用的理论模拟(Ⅰ)

本文叙述用一维非平衡辐射流体力学激光打靶程序模拟计算高功率密度(~10¹³W/cm²)激光照射中Z介质薄靶形成的等离子体状态。考虑的物理过程有轫致、光电离、电子碰撞电离及它们的逆过程,Compton散射过程等。Compton散射采用Fokker-Planck近似;电子和离子热传导采用限流扩散近拟;光子方程采用多群限流扩散近似;用平均原子模型计算布居数。激光的吸收主要考虑逆轫致吸收。用功率密度分别为5×10¹³W/cm²和1×10¹⁴W/cm²,波长0.53μm,脉宽450ps的激光从两面和单面打se薄靶,模拟计算结果与国外的实验结果^[1]一致。     

一种可用于极化~3He实验的新型磁场系统

原子核自旋极化的~3He气体已被深入研究并广泛用于各种科学实验.在过去的极化~3He实验中,为了减小磁场梯度对纵向弛豫时间的影响,通常会建造大尺寸的亥姆霍兹线圈来提供所需均匀度的主磁场环境.本文通过计算得到了新的六正方形线圈系统,可以为极化~3He实验提供小型高均匀性的磁场装置.其中线圈系√统内部超过30%的区域磁场梯度满足(|▽B_x|~2+|▽B_y|~2)/B_0 10~(-4)cm~(-1),这一均匀区域比例超过了现在所有用于极化~3He实验的线圈装置.对于其他需要大均匀区域磁场环境的研究实验,新的六线圈系统也具有很好的应用价值.     

Effective activation energy Ue(T,J,H) in textured Bi1.84Pb0.4Sr2Ca2Cu3Oy silver-clamped thick films

We have measured the resistivity of textured Bi_1.84Pb_0.4Sr₂Ca₂Cu₃O_y silver-clamped thick films as a function of temperature, current density ranging from 10 to 1×10³ A/cm² and magnetic field up to 0.3 T. We find that the effective activation energy U_e follows U_e(T,J,H)=U₀(1−T/T_p)^mln(J_c0/J)H⁻ with m=1.75 for Hab-plane and 2.5 for Hc-axis and =0.76 for Hab and 0.97 for Hc, for the current density regime above 100 A/cm², where T_p is a function of applied magnetic field and current density. This result suggests the effective activation energy U_e be correlated with the temperature, current density and magnetic field. The possible dissipative mechanisms responsible for the temperature, current density and magnetic field dependence of the effective activation energy are discussed.