~(87)Rb玻色-爱因斯坦凝聚体的快速实验制备

采用二维磁光阱产生了-个快速~(87)Rb原子流,并在高真空的三维磁光阱中实现了~(87)Rb原子的快速俘获,进一步采用射频蒸发冷却技术实现了原子云的预冷却,然后将原子转移到远失谐的光学偶极阱中蒸发得到了玻色-爱因斯坦凝聚体.实验上可以在25 s内完成三维磁光阱的装载(约1.0×10~(10)个~(87)Rb原子),然后经过16 s的冷却过程最终在光学偶极阱中获得5.0×10~5个原子的玻色-爱因斯坦凝聚体.实验重点研究了二维磁光阱的优化设计和采用蓝失谐大功率光束对四极磁阱零点的堵塞,抑制四极磁阱中原子的马约拉纳损耗,更加有效地对原子云进行预冷却.     

基于红失谐高斯光束的冷原子束流长距离传输

提出了一种利用红失谐高斯光束偶极力实现二维磁光阱长距离传输冷原子束的方案.利用二能级原子所受散射力公式分析并构造了87 Rb原子在光偶极阱二维磁光阱(2D-ODT MOT)中的受力公式,考虑了原子与背景气体碰撞的影响,利用四阶龙格-库塔法求解原子运动方程,获得原子的运动轨迹,统计并求出原子在不同高斯光束失谐以及功率条件作用下进入差分泵浦范围的原子数.实验验证了在红失谐高斯光束与原子束推送光相互组合的4种工作状态下科学实验腔中磁光阱冷原子装载情况.理论与实验结果表明:基于红失谐高斯光束的二维磁光阱长距离传输冷原子束的效果提升显著,科学腔原子装载效率明显提升、原子数目明显增加.     

以慢原子束方式进行原子转移的双磁光阱系统

建立了一套用于玻色-爱因斯坦凝聚实验的铷原子双磁光阱装置.从低速强源中获得慢原子束，向超高真空磁光阱进行原子转移.低速强源磁光阱与超高真空磁光阱之间可维持3个量级的压强差,超高真空磁光阱的真空度最高可达1×10^-9 Pa. 慢原子束的束流通量达1×10⁹/s. 约4×10⁸个⁸⁷Rb原子被装载到超高真空磁光阱中.还讨论了两种典型情况下磁光阱中装载的最大原子数.     

高通量冷原子束流的实现与测量

我们在实验上基于铯原子的2D+磁光阱获得了通量为8.5×1010原子/s、平均速度与速度分布分别为16 m/s与4 m/s、空间发散角为25 mrad的冷原子束流,通过相敏的飞行时间法对原子束流的通量进行了准确测量,并对背景原子气压、推送光功率以及冷却光失谐等参量对原子束流的影响进行了实验研究与分析.     

基于二维磁光阱的增强型199Hg冷原子团制备

在精密测量领域中,高效地制备冷原子团具有重要的意义.在光晶格钟里,缩短冷原子团的制备时间可以降低Dick噪声,从而提高光晶格钟的稳定性.本文采用二维磁光阱加推送光的构型提高了三维磁光阱在超高真空环境中的装载率,并通过压缩磁光阱技术降低了原子团温度,实现了用于¹⁹⁹Hg光晶格钟的增强型冷原子团制备.实验上通过优化三维和二维磁光阱的失谐量和磁场梯度以及推送光的失谐量和功率等参数,将三维磁光阱的¹⁹⁹Hg冷原子装载率增强了51倍,提升至3.1×10⁵ s^–1,然后使用压缩磁光阱技术将¹⁹⁹Hg冷原子团的温度降低至45μK,低于多普勒冷却理论温度.这种基于二维磁光阱的增强型冷原子团制备可在超真空环境下实现对三维磁光阱装载率的高增益,有效地缩短了冷原子团的制备时间,同时也降低了原子团的温度,有利于提高光晶格的转移效率,为其他冷原子实验中冷汞原子团制备提供了有效方案.     

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     

重力对~(87)Rb冷原子四极磁阱装载的影响

文章研究了重力作用下对磁光阱中~(87)Rb原子进行偏振梯度冷却后重新四极磁阱俘获的影响。研究了竖直放置四极线圈和水平放置四极线圈两种情形下,重力对原子偏振梯度冷却后四极磁阱重新俘获过程的作用,通过原子自由飞行吸收成像,观测到了原子的振荡。分析计算了~(87)Rb原子|2,2〉态补偿重力时所需的磁场梯度B′,探究了磁场参数对于振荡现象的影响,从而选择了水平放置磁场线圈的方法,提高了原子偏振梯度冷却后四极磁阱的装载效率。     

大失谐连续输运激光情形下双磁光阱中冷原子的输运

在我们建立的铯原子双磁光阱实验装置上,采用连续激光将气室磁光阱中冷却并俘获的冷原子输运到超高真空磁光阱.在前期利用近共振弱光研究原子输运的工作基础上,我们将输运激光的负失谐量扩展到约2.0 GHz,并增大了输运光功率,对冷原子的输运作了实验研究.结果表明:在大负失谐情形下,较强的输运光使冷原子输运更为有效,归因于输运光束对原子的偶极力造成对冷原子的导引作用.     

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。     

采用消逝波干涉的二维表面微光阱阵列

提出了一种采用两套超大红失谐消逝波干涉和一束蓝失谐消逝波光场来实现原子二维表面微光阱阵列和原子有效强度梯度冷却的新方案,得到了二维表面微光阱阵列的光强分布和光学势分布.研究发现,二维表面微光阱阵列中微光阱的光学势能够有效地囚禁从标准磁光阱中释放的冷原子,并且被囚禁的冷原子能在蓝失谐消逝波光场的作用下产生有效的强度梯度Sisyphus冷却,对⁸⁷Rb原子而言,原子温度能被冷却到2.56μK.该方案在冷原子物理、原子光学和量子光学领域中有着广阔的应用前景. 关键词： 消逝波干涉 微光阱阵列 原子囚禁 强度梯度冷却     

利用铷原子双光子跃迁产生420nm蓝光的实验研究

本实验通过饱和吸收方法获得了铷原子5S_(1/2)→5 P_(3/2)单光子跃迁光谱,并进一步研究了铷原子5S_(1/2)→5 P_(3/2)→5 D_(5/2)的双光子跃迁光谱。使用780nm的控制光和776nm的信号光反向共线作用到铷泡中,通过探测6 P_(3/2)→5S_(1/2)自发辐射产生的420nm蓝光信号得到铷原子5S_(1/2)→5 P_(3/2)→5 D_(5/2)双光子跃迁光谱,利用法布里-珀罗干涉仪测量了~(87)Rb和~(85)Rb的5 D_(5/2)激发态超精细能级,详细研究了铷泡温度和776nm信号光功率对~(87)Rb 5S_(1/2)(F=2)→5 D_(5/2)双光子跃迁光谱的影响。该研究工作为基于原子分子精密光谱测量提供了实验基础。     

Probing the quantum state of a guided atom laser pulse

We describe bichromatic superradiant pump-probe spectroscopy as a tomographic probe of the Wigner function of a dispersing particle beam. We employed this technique to characterize the quantum state of an ultracold atomic beam, derived from a 87Rb Bose-Einstein condensate, as it propagated in a 2.5 mm diameter circular waveguide. Our measurements place an upper bound on the longitudinal phase space area occupied by the 3 x 10(5) atom beam of 9(1)Planck's constant and a lower bound on the coherence length of L>or=13(1) microm. These results are consistent with full quantum degeneracy after multiple orbits around the waveguide.     

Time-resolved probing of the ground state coherence in rubidium

We demonstrate the preparation and probing of the coherence between the hyperfine ground states |S(1/2),F=1> and |5S(1/2),F=2> of the Rb87 isotope. The effects of various coherence control techniques, i.e., fractional stimulated Raman adiabatic passage and coherent population return, on the coherence are investigated. These techniques are implemented using nearly degenerate pump and Stokes lasers at 795 nm (Rb D1 transition), which couple the two hyperfine ground states via the excited state |5P(1/2),F=1> through a resonant two-photon process in which a coherent superposition of the two hyperfine ground states is established. The medium is probed by an additional weak laser, which generates a four-wave mixing signal proportional to the ground state coherence and allows us to monitor its evolution in time. The experimental data are compared with numerical simulations.     

Light self-trapping in a large cloud of cold atoms

We show that, for a near-resonant propagating beam, a large cloud of cold Rb87 atoms acts as a saturable Kerr medium and produces self-trapping of light. By side fluorescence imaging, we monitor the transverse size of the beam and, depending on the sign of the laser detuning with respect to the atomic transition, we observe self-focusing or self-defocusing, with the waist remaining stationary for an appropriate choice of parameters. We analyze our observations by using numerical simulations based on a simple two-level atom model.     

Dynamics of F=2 spinor Bose-Einstein condensates

We experimentally investigate and analyze the rich dynamics in F=2 spinor Bose-Einstein condensates of 87Rb. An interplay between mean-field driven spin dynamics and hyperfine-changing losses in addition to interactions with the thermal component is observed. In particular, we measure conversion rates in the range of 10(-12) cm(3) s(-1) for spin-changing collisions within the F=2 manifold and spin-dependent loss rates in the range of 10(-13) cm(3) s(-1) for hyperfine-changing collisions. We observe polar behavior in the F=2 ground state of 87Rb, while we find the F=1 ground state to be ferromagnetic. We further see a magnetization for condensates prepared with nonzero total spin.     

Rb原子滤波器的实验研究

本文用热Rb原子进行了光学滤波的研究。将一束激光调谐到Rb原子D2线的F=1→F′=2共振吸收线上,使其泵浦Rb原子,实现原子布居极化(即将Rb原子制备到能级F=2上)。当一束信号光反向穿过该介质时,若信号光频率调谐到原子"吸收窗口"(D1线F=2→F′=2),该介质对信号光大量吸收,信号光透射率仅为0.14%;若信号光频率调谐到原子"透明窗口"(D1线F=1→F′=2),信号光透射率高于47.4%。这种极化的原子介质可以用来做光学滤波器。     

Improved method to retrieve aerosol optical properties from combined elastic backscatter and Raman lidar data

Two methods to load a microtrap consisting of two concentric microwire loops of radii 300 and 660 μm carrying oppositely oriented currents are demonstrated. Atoms can be directly loaded into the microtrap from a surface magneto-optical trap or alternatively using a far-off resonance optical dipole trap (FORT) as an intermediate step. About 1 × 10^{5 87}Rb atoms can be loaded into the microtrap using either technique although the FORT achieves a lower temperature. The FORT is well suited to loading a linear array of 3 microtraps that are aligned with the propagation direction of the infrared laser. Atoms can be trapped in either the $5S_{1/2}\;F=1$ or 2 ground state hyperfine level. The position of the microtrapped atom cloud can be precisely adjusted using a bias magnetic field over a distance of 350 to slightly <50 μm from the atom chip surface.     

Ultra-Slow Atomic Beam Generation by Velocity Selective Resonance

We describe a method to generate an ultra-slow atomic beam by velocity selective resonance （VSR）. A VSR experiment on a metastable helium beam in a magnetic field is presented and the results show that the transverse velocity of the deflected beam can be cooled and precisely controlled to less than the recoil velocity, depending on the magnitude of the magnetic field. We extend this idea to a cold atomic cloud to produce an ultra-slow 87Rb beam that can be used as a source of an atomic fountain clock or a space clock.     

Atomic vapor cells for chip-scale atomic clocks with improved long-term frequency stability

A novel technique for microfabricating alkali atom vapor cells is described in which alkali atoms are evaporated into a micromachined cell cavity through a glass nozzle. A cell of interior volume 1 mm3, containing 87Rb and a buffer gas, was made in this way and integrated into an atomic clock based on coherent population trapping. A fractional frequency instability of 6 x 10(-12) at 1000 s of integration was measured. The long-term drift of the F=1, mF=0-->F=2, mF=0 hyperfine frequency of atoms in these cells is below 5 x 10(-11)/day.     

Decoherence of electromagnetically induced transparency in atomic vapor

We report characterization of electromagnetically induced transparency (EIT) resonances in the D1 line of (87)Rb under various experimental conditions. The dependence of the EIT linewidth on the power of the pump field was investigated at various temperatures for the ground states of the lambda system associated with different hyperfine levels of the atomic 5S(1/2) state as well as magnetic sublevels of the same hyperfine level. Strictly linear behavior was observed in all cases. A theoretical analysis of our results shows that dephasing in the ground state is the main source of decoherence, with population exchange playing a minor role.