Collisions in a cesium hybrid optical and magnetic trap

A new scheme for trapping Cs atoms in a non dissipative trap has been developed. The trap involves both optical dipole forces and magnetic forces. This device is suitable for Cs atoms in the lowest energy Zeeman sublevel, thus avoiding the two-body inelastic collisions which prevented reaching Bose-Einstein condensation of Cs in purely magnetic traps. Furthermore, an additional magnetic field can be applied, allowing a fine tuning of the two-body elastic collision cross-section. We report on the experimental realization of such a trap and describe the characteristics of the trapped atomic sample. An analysis of the collisional regime is performed using measurements of the damping of the oscillatory modes of the trapped atom cloud.     

Light-induced evaporative cooling in a magneto-optical trap

This paper presents an experimental demonstration of light-induced evaporative cooling in a magneto-optical trap. An additional laser is used to interact with atoms at the edge of the atomic cloud in the trap. These atoms get an additional force and evaporated away from the trap by both the magnetic field and laser fields. The remaining atoms have lower kinetic energy and thus are cooled. It reports the measurements on the temperature and atomic number after the evaporative cooling with different parameters including the distance between the laser and the centre of the atomic cloud, the detuning, the intensity. The results show that the light-induced evaporative cooling is a way to generate an ultra-cold atom source.     

Investigation of sub-Doppler cooling effects in a cesium magneto-optical trap

We present an investigation of sub-Doppler effects in a cesium magneto-optical trap. First, a simple one-dimensional theoretical model of the trap is developed for aJ _g = 1 J _e = 2 transition. This model predicts the size of the trapped atom cloud and temperature as a function of laser intensity and detuning. In the limit of small magnetic field gradients, the trap temperature is found to be equal to the molasses temperature and a minimum size for the trap is calculated. We then describe several experiments performed in a three-dimensional cesium trap to measure the trap parameters, spring constant, friction coefficient, temperature and density. Whilst the temperature of the trapped atoms is found to be equal to the molasses temperature, in agreement with theory, the trap spring constant is found to be two orders of magnitude smaller than the one-dimensional prediction, a value close to that predicted by Doppler models. The maximum density is found to be on the order of 10¹² atoms/cm³ or one atom per optical wavelength on average. When the number of trapped atoms becomes large, the temperature begins to increase dramatically. This excess temperature depends in a very simple way on the atom number, laser intensity and detuning, suggesting that its origin lies in multiple photon scattering within the trap.     

Quantum effects in a one-dimensional magnetic gravitational trap for ultracold neutrons

JETP Letters - The problem of storing ultracold neutrons over a plane magnetic mirror in the presence of gravity is considered. For neutrons with a definite polarization, the sum of the magnetic...     

Evaporative cooling of cesium atoms in the gravito-optical surface trap

We report on cooling of an atomic cesium gas closely above an evanescent-wave atom mirror. Our first evaporation experiments show a temperature reduction from 10 μK down to 300 nK along with a gain in phase-space density of almost two orders of magnitude. In a series of measurements of heating and spin depolarization an incoherent background of resonant photons in the evanescent-wave diode laser light was found to be the limiting factor at this stage.     

一维谐振腔中的理想玻色气体的热力学性质

一维谐振腔中的理想玻色气体没有相变,但是在低温下存在玻色-爱因斯坦凝聚体.在高温情况下,该体系的内能等于力一位移的乘积;关于微观状态数计算,传统的方法有所不足,本文给出了正确方法.     

Stark-potential evaporative cooling of polar molecules in a novel optical-access opened electrostatic trap

We propose a novel optical-access opened electrostatic trap to study the Stark-potential evaporative cooling of polar molecules by using two charged disk electrodes with a central hole of radius r0= 1.5 mm, and derive a set of new analytical equations to calculate the spatial distributions of the electrostatic field in the above charged-disk layout. Afterwards, we calculate the electric-field distributions of our electrostatic trap and the Stark potential for cold ND3 molecules, and analyze the dependences of both the electric field and the Stark potential on the geometric parameters of our charged-disk scheme,and find an optimal condition to form a desirable trap with the same trap depth in the x, y, and z directions. Also, we propose a desirable scheme to realize an efficient loading of cold polar molecules in the weak-field-seeking states, and investigate the dependences of the loading efficiency on both the initial forward velocity of the incident molecular beam and the loading time by Monte Carlo simulations. Our study shows that the maximal loading efficiency of our trap scheme can reach about 95%, and the corresponding temperature of the trapped cold molecules is about 28.8 m K. Finally, we study the Stark-potential evaporative cooling for cold polar molecules in our trap by the Monte Carlo method, and find that our simulated evaporative cooling results are consistent with our developed analytical model based on trapping-potential evaporative cooling.     

Efficient loading of cesium atoms in a magnetic levitated dimple trap

We report a detailed study of magnetically levitated loading of ultracold ¹³³Cs atoms in a dimple trap. The atomic sample was produced in a combined red-detuned optical dipole trap and dimple trap formed by two small waist beams crossing a horizontal plane. The magnetic levitation for the ¹³³Cs atoms forms an effective potential for a large number of atoms in a high spatial density. Dependence of the number of atoms loaded and trapped in the dimple trap on the magnetic fiel...     

Atomic hydrogen cooling under adiabatic expansion in a magnetic trap

A new method for cooling atomic hydrogen down to 100 μK or below is suggested. The method exploits the unique properties of atomic hydrogen, which are the following: atomic hydrogen does not condense at temperatures as low as 20 μK and cannot be heated by IR radiation in the absence of atom-wall collisions. Therefore, the most efficient and well-known gas cooling technique can be employed, namely, the adiabatic expansion of the volume occupied by the gas (this approach is used in a gas-expansion machine). It is suggested to adiabatically expand the volume of a magnetic trap containing atomic hydrogen.     

Mean-field model for Josephson oscillation in a Bose-Einstein condensate on an one-dimensional optical trap

Using the axially-symmetric time-dependent Gross-Pitaevskii equation we study the phase coherence in a repulsive Bose-Einstein condensate (BEC) trapped by a harmonic and an one-dimensional optical lattice potential to describe the experiment by Cataliotti et al. on atomic Josephson oscillation [Science 293, 843 (2001)]. The phase coherence is maintained after the BEC is set into oscillation by a small displacement of the magnetic trap along the optical lattice. The phase coherence in the presence of oscillating neutral current across an array of Josephson junctions manifests in an interference pattern formed upon free expansion of the BEC. The numerical response of the system to a large displacement of the magnetic trap is a classical transition from a coherent superfluid to an insulator regime and a subsequent destruction of the interference pattern in agreement with the more recent experiment by Cataliotti et al. [New J. Phys. 5, 71 (2003)].Received: 20 March 2003, Published online: 30 July 2003PACS: 03.75.-b Matter waves - 03.75.Lm Tunneling, Josephson effect, Bose-Einstein condensates in periodic potentials, solitons, vortices and topological excitations - 03.75.Kk Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow     

Mixture of ultracold lithium and cesium atoms in an optical dipole trap

We present the first simultaneous trapping of two different ultracold atomic species in a conservative trap. Lithium and cesium atoms are stored in an optical dipole trap formed by the focus of a CO₂ laser. Techniques for loading both species of atoms are discussed and observations of elastic and inelastic collisions between the two species are presented. A model for sympathetic cooling of two species with strongly different mass in the presence of slow evaporation is developed. From the observed Cs-induced evaporation of Li atoms we estimate a cross-section for cold elastic Li-Cs collisions. Received: 1 August 2001 / Published online: 23 November 2001     

三维光学晶格中铯原子的装载与冷却

建立了四光束的三维光学晶格势场,在铯原子磁光阱和光学粘团的基础上实现了红失谐三维光学晶格中冷原子的装载.借助于短程飞行时间吸收谱测量冷原子温度,通过改变光学晶格的总光强和频率失谐等条件,对光学晶格中铯原子的亚多普勒冷却以及光学晶格中冷原子的寿命进行了研究. 关键词： 光学晶格 磁光阱 光学粘团 冷原子     

Sympathetic cooling of polyatomic molecules with S-state atoms in a magnetic trap

We present a rigorous theoretical study of low-temperature collisions of polyatomic molecular radicals with (1)S(0) atoms in the presence of an external magnetic field. Accurate quantum scattering calculations based on ab initio and scaled interaction potentials show that collision-induced spin relaxation of the prototypical organic molecule CH(2)(X(3)B(1)) (methylene) and nine other triatomic radicals in cold (3)He gas occurs at a slow rate, demonstrating that cryogenic buffer-gas cooling and magnetic trapping of these molecules is feasible with current technology. Our calculations further suggest that it may be possible to create ultracold gases of polyatomic molecules by sympathetic cooling with alkaline-earth atoms in a magnetic trap.     

应用于铯原子喷泉钟的二维磁光阱研制

理论模拟研究了二维磁光阱原子束流量与饱和蒸汽压、冷却光强、激光失谐量的关系, 构建了二维磁光阱(2D-MOT)装置, 实验上实现了大流量的慢速原子束, 其测量值为2.1× 10⁹/s.利用荧光法测量了各实验参数与流量的关系, 测量结果与数值模拟结果符合较好. 关键词： 2D-MOT 流量 慢速原子束 铯原子喷泉钟     

Bose-Einstein condensates in the presence of a magnetic trap and optical lattice

In this paper we consider solutions of a nonlinear Schrodinger equation with a parabolic and a periodic potential motivated from the dynamics of Bose-Einstein condensates. Our starting point is the corresponding linear problem which we analyze through regular perturbation and homogenization techniques. We then use Lyapunov-Schmidt theory to establish the persistence and bifurcation of the linear states in the presence of attractive and repulsive nonlinear inter-particle interactions. Stability of such solutions is also examined and a count is given of the potential real, complex and imaginary eigenvalues with negative Krein signature that such solutions may possess. The results are corroborated with numerical computations.     

Intense source of cold cesium atoms based on a two-dimensional magneto–optical trap with independent axial cooling and pushing

We report our studies on an intense source of cold cesium atoms based on a two-dimensional(2D) magneto–optical trap(MOT) with independent axial cooling and pushing.The new-designed source,proposed as 2D-HP MOT,uses hollow laser beams for axial cooling and a thin pushing laser beam to extract a cold atomic beam.With the independent pushing beam,the atomic flux can be substantially optimized.The total atomic flux maximum obtained in the 2D-HP MOT is4.02 × 1010atoms/s,increased by 60 percent compared to the traditional 2D+MOT in our experiment.Moreover,with the pushing power 10 μW and detuning 0Γ,the 2D-HP MOT can generate a rather intense atomic beam with the concomitant light shift suppressed by a factor of 20.The axial velocity distribution of the cold cesium beams centers at 6.8 m/s with an FMHW of about 2.8 m/s.The dependences of the atomic flux on the pushing power and detuning are studied in detail.The experimental results are in good agreement with the theoretical model.