用于原子干涉仪实验的锂原子的塞曼减速与磁光囚禁

为了制备适于原子干涉仪实验的低温锂原子样品,开展了锂原子的塞曼减速及与磁光阱囚禁相关的实验研究.设计并实现了一种结构紧凑的腔体内冷式多级线圈叠加的塞曼减速器,将速度小于600 m/s的7Li原子减速到60 m/s,磁光阱装载速率为5×108/s,囚禁原子数目1×109个,原子团的最低温度约为220±30μK.研究了光学黏胶中7Li原子的寿命与囚禁光频率失谐量的关系.这些结果为进一步开展7Li原子亚多普勒冷却、光势阱蒸发冷却以及原子干涉仪实验奠定了基础.     

Narrow-line magneto-optical cooling and trapping of strongly magnetic atoms

Laser cooling on weak transitions is a useful technique for reaching ultracold temperatures in atoms with multiple valence electrons. However, for strongly magnetic atoms a conventional narrow-line magneto-optical trap (MOT) is destabilized by competition between optical and magnetic forces. We overcome this difficulty in Er by developing an unusual narrow-line MOT that balances optical and magnetic forces using laser light tuned to the blue side of a narrow (8 kHz) transition. The trap population is spin polarized with temperatures reaching below 2 muK. Our results constitute an alternative method for laser cooling on weak transitions, applicable to rare-earth-metal and metastable alkaline earth elements.     

近共振三维光学晶格中铯原子温度的参数依赖

介绍了四光束三维近共振光学晶格的方案,在铯原子磁光阱和光学粘团的基础上搭建了近共振光学晶格的光路,实现了光学晶格中冷原子的装载.利用短程飞行时间吸收法测量了近共振光学晶格中冷原子的温度,通过改变晶格的光强和失谐等条件,对近共振光学晶格中铯原子的亚多普勒冷却的参数依赖关系作了实验研究,并与光学粘团作了比较.     

Spectral characteristics of cold rubidium atoms in a dark magneto-optical trap

Spectral characteristics of rubidium atoms confined in a dark magneto-optical trap (DMOT) are measured, including probe absorption spectra and atom density as a function of the cooling and repumping laser frequencies. The trap can capture and cool more than 2.5 × 10⁸ rubidium atoms, confining them in a hyperfine state weakly perturbed by the laser beams used to form the trap. The optical density of the trapped atomic cloud approaches 9. A qualitative model of the DMOT operation is presented, based on the experimental results obtained.     

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     

磁光阱中单原子荧光信号的优化及单原子的高效装载

实验中首先通过增大四极磁场梯度、提高背景真空度、缩小冷却俘获激光光束直径的方法获得了磁光阱中单原子的装载.其次,通过减小冷却光失谐量、适当增加其光强、同时使用偏振光谱锁频技术抑制冷却光噪声的方法得到了磁光阱中高信号背景比的单原子荧光信号.此外,通过实时反馈控制磁光阱四极磁场梯度的方法,在实验中实现了单原子98%的装载概率.使用Hamburg Brown-Twiss方案测量了磁光阱中的单原子在连续光激发下所辐射荧光的光子统计特性,得到二阶关联度g(2)(τ=0)=0.09.     

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.     

Novel 1D optical molasses composed of two elliptical Gaussian beams with an ultrahigh orbital angular-momentum

We propose a novel scheme to form a 1D optical molasses by using two counter-propagating red-detuned elliptical Gaussian beams possessing an ultrahigh orbital angular-momentum. In this optical molasses, atoms will suffer both an axial and an azimuthal Doppler cooling, and their temperature can be far below the conventional Doppler cooling limit, which provides a new opportunity for the laser cooling of the most abundant bosonic isotopes of alkaline-earth atoms. Because these atoms lack the hyperfine structure, they cannot be cooled by the well-known sub-Doppler cooling schemes.     

Laser cooling of thulium atoms

We demonstrated laser cooling and trapping of thulium atoms at sub-Doppler temperatures in a magneto-optical trap (MOT). Up to 3 × 10⁶ thulium atoms were trapped in the MOT at temperatures down to 25(5) μK which is approximately 10 times lower than the Doppler limit. The lifetime of atoms in the MOT varied between 0.3–1.5 s and was restricted mostly by optical leaks from the upper cooling level. The lower limit for the leaking rate was estimated to be 22(6) s⁻¹. Due to a big magnetic moment of Tm atoms, a part of them were trapped in a magnetic trap from the quadrupole field of the MOT. We observed about 3 × 10⁴ purely magnetically trapped atoms at temperature of 25 μK with a lifetime in the trap of 0.5 s. Also we set up a “dark” MOT consisting of six crossed hollow beams which increased the number of trapped atoms by a factor of 5 leading to 1.5 × 10⁷ atoms at the expense of higher temperature.     

A cold 87Rb atomic beam

We demonstrate an experimental setup for the production of a beam source of cold ⁸⁷Rb atoms. The atoms are extracted from a trapped cold atomic cloud in an unbalanced three-dimensional magneto-optical trap. Via a radiation pressure difference generated by a specially designed leak tunnel along one trapping laser beam, the atoms are pushed out continuously with low velocities and a high flux. The most-probable velocity in the beam is varied from 9 m/s to 19 m/s by varying the detuning of the trapping laser beams in the magneto-optical trap and the flux can be tuned up to 4×10⁹ s^-1 by increasing the intensity of the trapping beams. We also present a simple model for describing the dependence of the beam performance on the magneto-optical trap trapping laser intensity and the detuning.     

Production and guidance of pulsed atomic beams on chip

We demonstrated two experimental methods of producing and guiding pulsed atomic beams on chip. One is to trap atoms first in a U-type magneto-optical trap on the chip, then transfer them to the magnetic guide field and push them simultaneously by a continuous force from the power imbalance of the magneto-optical trap laser beams hence the pulsed cold atom beams are produced and move along the magnetic guide to the destination. The other is to trap atoms directly by a H-type magneto-optical trap, then push them to make them move along the magnetic guide field, thus high rate cold atom beams can be produced and guided on the chip.     

An optical conveyor belt for single neutral atoms

Using optical dipole forces we have realized controlled transport of a single or any desired small number of neutral atoms over a distance of a centimeter with sub-micrometer precision. A standing wave dipole trap is loaded with a prescribed number of cesium atoms from a magneto-optical trap. Mutual detuning of the counter-propagating laser beams moves the interference pattern, allowing us to accelerate and stop the atoms at preselected points along the standing wave. The transportation efficiency is close to 100%. This optical ‘single-atom conveyor belt’ represents a versatile tool for future experiments requiring deterministic delivery of a prescribed number of atoms on demand. Received: 6 July 2001 / Published online: 23 November 2001     

Beyond optical molasses: 3D raman sideband cooling of atomic cesium to high phase-space density

We demonstrate a simple, general purpose method to cool neutral atoms. A sample containing 3x10(8) cesium atoms prepared in a magneto-optical trap is cooled and simultaneously spin polarized in 10 ms at a density of 1.1x10(11) cm (-3) to a phase space density nlambda(3)(dB) = 1/500, which is almost 3 orders of magnitude higher than attainable in free space with optical molasses. The technique is based on 3D degenerate Raman sideband cooling in optical lattices and remains efficient even at densities where the mean lattice site occupation is close to unity.     

Power Broadening of Two-Photon Coherent Resonances on Rydberg Atomic Transitions in a Magneto-Optical Trap

We study power broadening of coherent two-photon resonances on Rydberg transitions in lithium-7 atoms in a magneto-optical trap (MOT). We apply the spectroscopic technique based on the reduction of resonance fluorescence in the MOT. One of the main contributions to the spectral broadening is associated with heating of the trapped atoms by laser cooling beams. We suggest a new nondestructive method to measure the atomic temperature in a working MOT using two-photon spectroscopy with variable directions of probe beams.     

Optical forces on neutral atoms in the presence of fluctuating laser fields: numerical analysis

Doppler cooling of ⁸⁸Sr atoms is studied in the presence of off-resonant red-detuned fluctuating laser fields.Using a semi-classical approach,we show that the relevant physical quantities in the cooling process,such as optical forces,the damping coefficient,Doppler temperature,and atom number in the trap,are strongly affected by the laser amplitude and phase fluctuations.We find that the Doppler cooling limit is higher than the predicted Doppler theory for non-fluctuating lasers.This ...     

Loading of a cold atomic beam into a magnetic guide

We demonstrate experimentally the continuous and pulsed loading of a slow and cold atomic beam into a magnetic guide. The slow beam is produced using a vapor loaded laser trap, which ensures two-dimensional magneto-optical trapping, as well as cooling by a moving molasses along the third direction. It provides a continuous flux larger than 10⁹ atoms/s with an adjustable mean velocity ranging from 0.3 to 3 m/s, and with longitudinal and transverse temperatures smaller than 100 μK. Up to 3×10⁸ atoms/s are injected into the magnetic guide and subsequently guided over a distance of 40 cm. Received 19 February 2002 Published online 28 June 2002     

~(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.     

EXPERIMENTAL STUDY ON LASER COOLING OF CESIUM ATOMS BY OPTICAL MOLASSES

We have studied the relationship between the temperature of Cs cold atoms and the parameters of the cooling laser. The atoms are first cooled and captured by a magnetooptical trap and then further coaled by optical molasses. The temperature of atoms la measured by a time-of-flight method. For relatively large laser intensity and small detuning, the temperature depends linearly on the intensity-to-detuning ratio, and nonlinear relationship has alao been found in other case.     

Laser cooling and magnetic trapping at several tesla

Laser cooling and magnetic trapping of (85)Rb atoms have been performed in extremely strong and tunable magnetic fields, extending these techniques to a new regime and setting the stage for a variety of cold atom and plasma experiments. Using a superconducting Ioffe-Pritchard trap and an optical molasses, 2.4 x 10(7) atoms were laser cooled to the Doppler limit and magnetically trapped at bias fields up to 2.9 T. At magnetic fields up to 6 T, 3 x 10(6) cold atoms were laser cooled in a pulsed loading scheme. These bias fields are well beyond an order of magnitude larger than those in previous experiments. Loading rates, molasses lifetimes, magnetic-trapping times, and temperatures were measured using photoionization and electron detection.     

Compact magneto-optical trap for rubidium atoms

The characteristics of a magneto-optical trap (MOT) using small-diameter cooling laser beams are considered. Trapping and cooling of Rb atoms from the surrounding gas of warm atoms takes place in the trap. A compact (140 μm) and stable atomic cloud is obtained with a density of 7 × 10¹⁰ cm^?3, which is three orders of magnitude higher than the density of the surrounding gas.