Efficient Loading Of Ultracold Sodium Atoms In Optical Dipole Trap

Bose–Einstein condensate(BEC)is an ultracold neutral atomic gas which was first observed experimentally more than 30 years ago,marking the beginning of a new and evolving field of ultracold quantum gas research.it is widely used in many fields such as many-body physics,quantum information science,precision measurement,quantum simulation and so on.In this thesis,I propose an experimental system and an optimal experimental scheme for the all-optical preparation of sodium spinor Bose–Einstein condensate.By using this scheme,the atomic number of pure BEC in crossed optical dipole trap can be increased by 5 times compared with some widely used schemes.Our investigations could be used in the efficient loading of other atomic species in an optical dipole trap.This paper systematically reviews and summarizes the development history of ultracold atoms,and discusses the principles and mechanisms of laser cooling and trapping from the viewpoint of basic physics.On this basis,the process of preparing sodium BEC was described in detail.The sodium atoms are slowed down by a Zeeman decelerator,then cooled and trapped by a magneto-optical trap(MOT)for 8 seconds.The initial atom number is about 6.23×10~9,and the temperature is about 235?K.Subsequently,the compressed magneto-optical trap was applied and further cooled by the"Optical Molasses"technology,effectively increase the atomic density,and realize the pre-cooling of sodium atomic sample.The number of atoms at this stage is 5.1×10~8 and the temperature of the atomic cloud is 45?k.Two high-power laser beams from a fiber laser are crossed to form an optical dipole trap,and sodium atoms are loaded into the optical dipole well for 450ms.The effects of optical trap light power on atomic number,temperature and phase space density are experimentally investigated.A simple theory was proposed and in good accordance with the experimental results of the loaded atomic numbers.Our results provide a further understanding of the loading process of optical dipole trap and laid the foundation for the generation of a sodium BEC with an optical dipole trap.Finally,we reduce the power of the dipole beam for forced evaporative cooling,and the potential of the dipole well decreases exponentially until about1.2×10~5 sodium BECs are produced.The number of BEC atoms obtained is of the same order of magnitude as that obtained in previous studies.Moreover,our experimental period is shorter than that of previous experiments;this shorter time is advantageous for experiments such as spin compression and spin coherence,which need to be repeated many times.