全光学冷却与囚禁133Cs原子玻色-爱因斯坦凝聚的可能性

综述了近年来有关蒸发冷却¹³³Cs原子样品的实验进展,分析了磁囚禁¹³³Cs原子玻色爱因斯坦凝聚(BEC)的困难,并在此基础上提出了一个全光型冷却与囚禁¹³³Cs原子BEC的新方案.该方案主要由一个来自半导体激光(λ=0852μm)的倒金字塔形中空光束重力光学囚禁(pyramidal-hollow-beam gravito-optical trap,缩写为PHB GOT)和一个来自Ar⁺激光(λ=05013μm)的圆锥形中空光束重力光学囚禁(conical-hollow-beam gravito-optical trap,缩写为CHB GOT)组成.在PHB GOT中,冷原子经历了一个有效的中空光束感应的Sisyphus冷却(也即强度梯度冷却)和抽运光感应的几何冷却,原子温度将被从磁光囚禁(MOT)温度(约为60μK)冷却至几个光子反冲极限(约为2μK);而在Ar⁺中空光束囚禁(CHB GOT)中,冷原子将被Raman冷却或速度选择相干粒子数囚禁技术(velocity-selection coherent population trap,缩写为VSCPT)进一步冷却至光子反冲极限以下,并被激光频率高于原子共振频率的(也即蓝失谐的)covering光束压缩.我们就PHB冷却的动力学过程进行了Monte-Carlo模拟,并计算了Ar⁺中空光束囚禁¹³³Cs原子的光学势.研究结果表明,实现一个全光学冷却与囚禁的¹³³Cs原子BEC是可能的 关键词： 倒金字塔型中空光束重力光学囚禁 强度梯度冷却 氩离子中空光束囚禁 喇曼冷却 铯原子BEC

POSSIBILITY OF ALL OPTICALLY-COOLED AND TRAPPED 133Cs ATOMIC BEC

The experimental progress on rf evaporative cooling of 133Cs atomic sample in recent year is reviewed, and the difficulty of magnetically trapped 133Cs atomic Bose-Einstein condensation (BEC) is analyzed. In this paper, we propose an all-optically-cooled and -trapped 133Cs BEC scheme, which is composed of a pyramidal-hollow-beam gravito-optical trap (PHB GOT) from a diode laser (λ=0.852 μm) and a conical-hollow-beam (CHB) GOT from an Ar+ laser (=0.5013 μm). In the PHB GOT, the cold atoms experience an efficient hollow-beam induced Sisyphus cooling (i.e., intensity gradient cooling) and repumpimg-beam induced geometric cooling, and they will be cooled to a few photon-recoil limits (～2 μK) from MOT's temperature (～60 μK). Whereas in the Ar+ hollow-laser-beam trap, cold atoms will be further cooled by Raman cooling (or velocity-selection coherent population trapping) and compressed by a blue-detuned covering beam. We have performed Monte-Carlo simulations for PHB cooling process, calculated the optical potential for 133Cs atoms in Ar+ hollow laser beam, and estimated total collision loss and atomic density. Our study shows that the realization of an optically-cooled and -trapped BEC of 133Cs atoms may be possible in our all-optical dipole trap.