铯原子双磁光阱中冷原子的输运：从推载到导引

在超高真空环境下实现中性原子的激光冷却与俘获，可以有效地避免背景气体对冷原子的碰撞所造成的影响，已成为玻色-爱因斯坦凝聚、冷原子光学腔量子电动力学、中性原子玻色-费米混合气体等实验研究的出发点。结合气室磁光阱和超高真空磁光阱的所谓双磁光阱，以其真空系统相对简单、参数易于控制、效率高等优点，得到了很大发展。双磁光阱既能在气室磁光阱部分从处于室温的原子背景中快速冷却和俘获原子，然后将其通过一定途径输运到超高真空磁光阱中，又能达到在压力极低的超高真空环境下制备冷原子的目的。     

中性原子的表面双磁光阱及其应用

提出了一种新的采用载流导线的表面双磁光阱(MOT)方案(即双U型导线磁光阱方案)。通过改变中间U型导线中的电流大小,即可将一个双磁阱连续地合并为一个单磁阱,反之亦然。详细计算和分析了上述双U型载流导线磁光阱方案的磁场及其梯度的空间分布,研究发现当导线中的电流为600 A,z方向均匀偏置磁感应强度为-4.0×10-3 T时,双U型导线方案产生的两个磁阱中心的磁场梯度约为1.5×10-3~2.5×10-3 T/cm,结合通常制备磁光阱时所用的三维粘胶(Molasses)光束即可在基底表面附近形成一双磁光阱。理论分析表明在弱光近似下,每个磁光阱中所能俘获的85Rb原子数约为106 量级,相应的磁光阱温度约为270μK。由于双磁光阱可以独立制备,所以双U型导线方案特别适用于制备双样品磁光阱,并用于研究双原子样品的冷碰撞性质。     

用吸收法对铯原子磁光阱中冷原子数目的测量

介绍了吸收法测量冷原子数的原理以及对铯原子气室磁光阱中俘获的冷原子数目的测量过程及结果. 与通常的荧光收集法相比，在原理上与静止二能级原子同共振单模光场作用的模型更加接近，同时大大减小了测量中的误差累积，提高了测量精度. 测得的冷原子数为(8±0.3)×10⁶，同时还利用测得的阱中俘获的稳态冷原子数和磁光阱中冷原子的寿命间接获得了磁光阱的俘获率. 关键词： 激光冷却与俘获 磁光阱 冷原子数目 俘获率     

Rb原子磁光阱中囚禁原子数目与实验参数的依赖关系

研究表明，Rb原子磁光阱中所囚禁的原子数目对囚禁光的光强和失谐量，回泵光的强度以及磁场梯度有很大的依赖关系.用二能级系统模型对囚禁原子数目随囚禁光的光强和失谐量的变化关系进行了预估，理论预测的结果与实验结果定性符合.实验结果也展示了囚禁原子数目随回泵光的强度和磁场梯度的变化关系，要定量解释这些实验结果则需要更复杂的理论模型.通过囚禁原子数目对实验参数依赖关系的研究，得到特定的实验参数，来获得最大数目的冷原子. 关键词： 磁光阱 冷原子     

磁光阱特性及冷原子集合行为的实验研究

磁光阱目前已经成为量子光学领域的内的一种强有力的研究工具，在实现了铯磁光阱后，我人通过对实验系统的改进提高了磁光阱的性能，在此基础上对磁光阱中原子数目和密度与磁光阱参数（包括激光光强，失谐以及磁场梯度等）的关系进行了系统的实验研究，结果与我们的理论预计大致符合，同时我们还观察到调节冷却激光光束准直和补偿地磁场的姆霍兹线圈电流过程中出现的冷原子云形状的变化，包括原子云的干涉图样，多亮点原子云，环形原     

采用原子汽室磁光阱技术实现铯原子的激光冷却与俘获

近１０年来，中性原子的激光冷却与俘获方面的研究极为活跃，取得了许多重要的进展。其中，１９９０年Ｗｉｅｍａｎ等人提出的直接工作在原子汽室中的磁光阱［１］，相对简化了原子冷却与俘获的装置和技术，使这方面的研究得以进一步推广和促进。由于冷原子在玻色－爱因斯...     

磁光阱中冷原子的实验特性

冷原子的获得对于原子物理的研究具有重要的意义,文章综述了激光冷却与囚禁原子技术发展以来对磁光阱中中性冷原子特性的研究进展,包括冷原子对光子的吸收与散射,冷原子之间的吸引与排斥导致的超冷碰撞与长程分子状态,朱子的非线性特性等。     

磁光阱中冷原子的实验特性

冷原子的获得对于原子物理的研究具有重要的意义,文章综述了激光冷却与囚禁原子技术发展以来对磁光阱中中性冷原子特性的研究进展,包括冷原子对光子的吸收与散射,冷原子之间的吸引与排斥导致的超冷碰撞与长程分子状态,冷原子的非线性特性等．     

冷原子的双阱微磁表面囚禁

提出了两种新颖的采用载流导线的双阱微磁表面囚禁方案(即双U形与双Z形导线囚禁)。通过改变囚禁方案中直导线中的电流方向，即可将双U形导线囚禁改变为双Z形导线囚禁；如果逐渐减小直导线中的电流大小，即可将一个双阱微磁囚禁连续地合并为一个单阱微磁囚禁，反之亦然。详细计算和分析了上述两种载流导线囚禁方案的磁场及其梯度的空间分布。研究发现在导线中通以较小的电流，即可在导线表面附近产生很大的磁场梯度及其曲率。例如当电流为O．2A时，其磁场梯度和曲率可分别达到0．2T／cm和10T／cm2以上。由于双U形导线囚禁中存在磁场零点，而双Z形导线囚禁中仅存在磁场最小值，所以双U形导线囚禁仅适用于制备双样品磁光囚禁(MOT)或研究中性原子的冷碰撞，而双Z形导线囚禁除了可用于研究原子的冷碰撞之外，还可以用于制备双样品玻色-爱因斯坦凝聚(BEC)或实验研究双阱玻色-爱因斯坦凝聚的性质等。     

一种测量磁光阱中冷原子密度和温度的新方法

报道了对磁光阱中冷铯原子吸收谱的实验观察,由于冷原子的多普勒增宽远小于激光发态超精细分裂,实验观察到三个孤立的吸收峰（Cs,6S1/2,F=4→6P3／2,F＝3,4,5,）其吸收系数比为3：7：12,这与相应跃迁振子强度一致。利用吸收信号测量了冷原子云的密度.结果与荧光探测法在10％的精度内符合;用吸收信号测量了冷原子的温度,测量结果与用荧光飞行时间法和释放捕捉法的结果吻合。     

A Single Folded Beam Magneto-Optical Trap System for Neutral Mercury Atoms

Mercury is a promising candidate for the optical lattice clock,due to its low sensitivity to the blackbody radiation.We develop a single folded beam magneto-optical trap for the neutral mercury optical lattice clock,with a 253.7nm frequency quadrupled laser.Up to 1.7 × 10~6(~(202)Hg) or 1.5 × 10~6(~(199)Hg) atoms can be captured,and the atom temperature is lowered to 170μK(~(202)Hg) or 50μK(~(199)Hg).The cold atom signals of all six rich abundant isotopes are observed in this system.     

Experimental Properties of Optical Phase Conjugation in Cold Atoms in a Magneto-Optical Trap

We employ a sample of cold 87Rb atoms in a magneto-optical trap to study the impulse responses and spatial characters of backward conjugate waves in a four-wave mixing process. We measure the slow and superluminal group velocities of backward conjugate waves, and find the sensitive variation of the spatial mode of backward waves with the probe-pump detuning and the dependence of the reflectance on the magnetic field, while the trapping magnetic field exists.     

Enhancement of Transfer Efficiency of Cold Atoms Using an Optical Guiding Laser Beam

We transfer cold ^87 Rb atoms from a vapour cell chamber to a spatially separated UHV magneto-optical trap （MOT） with the assistance of a red-detuned optical guiding beam and a normal push beam. Efficient optical guiding of the cold atoms is observed within a small detuning window. A pulsed optical guiding beam enhances the transfer efficiency and hence allows us to collect more atoms in UHV MOT in a shorter time, which is favourable for our experiment of achieving Bose-Einstein condensates （BEC）. Besides the easy operation, another advantage of this optical guiding technique is also demonstrated such that slower atomic beams may be efficiently transferred along horizontal direction. This study is a direct application of the optical guiding technique as a powerful tool.     

大磁场梯度铯原子磁光阱中单原子的实验观测

基于中性原子的激光冷却与俘获技术,目前人们已可以对单个原子的外部乃至内部自由度进行有效的调控.从而可在单原子单光子的层次上对光场与物质的相互作用进行研究.     

Magneto-Optical Trapping of Ytterbium Atoms with a 398.9nm Laser

We report the realization of ytterbium magneto-optical trap （MOT） operating on the dipole-allowed ^1S0 - ^1P1 transition at 398.9nm. The MOT is loaded by a slowed atomic beam produced by a Zeeman slower. All seven stable isotopes of Yb atoms could be trapped separately at different laser detuning values. Over 10^7 174 Yb atoms are collected in the MOT, whereas the atom number of fermionic isotope ^171Yb is roughly 2.3 × 10^6 due to a lower abundance. Without the Zeeman slower the trapped atom numbers are one order of magnitude lower. Both the even and odd isotopes are recognized as excellent candidates of optical clock transition, so the cooling and trapping of ytterbium atoms by the blue MOT is an important step for building an optical clock.     

Temperature of the Remaining Cold Atoms after Two-Step Photoionization in an ^87Rb Vapor Cell Magneto-Optical Trap

The temperature of the remaining cold ^87Rb atoms confined in a vapor cell magneto-optical trap after two-step photoionization has been measured. In the two-step photoionization process, the first excitation laser is served by the cooling laser and the second excitation laser is served by a continuous semiconductor laser with a wavelength of 450hm. The results show that the temperature of the remaining cold atoms decreases as the intensity of the second excitation laser increases. Moreover, the relationship between the temperature T and number N of the remaining cold atoms generally foliows a power law, while it deviates from the well-known T ∝ N^1/3 and the power factor is smaller than 1/3. We propose that ion-atom collisions occurring during a photoionization process strongly influence the temperature sealing law in an optiealiy dense magneto-optical trap in the presence of an ionization laser. In addition, the forced evaporative cooling due to the combined effect of the detuning of the first excitation laser and the two-step photoionization plays a role in cooling the remaining cold atoms and results in the dependence of the power factor on the detuning of the first excitation laser.     

Two Cold Atoms in a Harmonic Trap

Two ultracold atoms moving in a trap interact weakly at a very short distance. This interaction can be modeled by a properly regularized contact potential. We solve the corresponding time-independent Schrödinger equation under the assumption of a parabolic, spherically symmetric trapping potential.     

Directly Trapping Atoms in a U-Shaped Magneto-Optical Trap Using a Mini Atom Chip

We experimentally demonstrate the trapping of ^85Rb atoms directly on a chip-size U-shaped magneto-optical trap （U-MOT）. The trap includes a U-shaped wire on the chip, two bias magnetic field coils and laser beams. The capture volume of the U-MOT is theoretically calculated, and the trap is experimentally realized. With 2 A current applied to the U-shaped wire and 2-Gauss horizontal bias field, more than 2 × 10^6 atoms are trapped. In contrast with an ordinary mirror-MOT, this U-MOT captures atoms directly from the background, thus the trap size is greatly reduced. Based on this mini trap scheme, it is possible to realize a chip-size atom trap array for quantum information processing.