Research On The Coherent Manipulation And Photoassociation Of Quantum Degenerate Gases

Since the experimental realization of the Bose-Einstein Condensates(BEC)in 1995,the BEC has become the best platform for quantum simulation and quantum precision measurement.The spinor Bose-Einstein condensate can be used to study quantum magnetism,superfluid,strong correlation,spin squeezing and quantum entanglement because of its spin degrees of freedom.We designed and built an experimental system for preparing spinor Bose-Einstein condensates.The system has an ultra-high vacuum degree and uses a Zeeman slower to pre-cool the atoms.Then we propose an all-optical method to prepare spinor Bose-Einstein condensates by directly evaporation in a dipole trap.This method shortens our experimental period and improves the efficiency and stability of the preparation.Based on this,we employed microwave and radio frequency to realize the coherent preparation and manipulation of spinor BEC.We propose a novel method to measure the trapping frequency of dipole traps by manipulating the spin current.It solves the problem that it is difficult to accurately measure the trapping frequency in small waist dipole traps,optical tweezers and strongly damped traps.Spin-1 condensates manifests in either antiferromagnetic or ferromagnetic properties,depending on the spin interactions and properties.In the photoassociation(PA)spectrum of the spinor Bose-Einstein condensate,there are adjacent molecular states which are formed by different scattering channels.Through these scattering channels,the strength of the spin interactions can be modulated,and then controlling the magnetic properties of the system.The simulation of quantum magnetism is of great significance to the study of magnetic systems and superfluid phase transitions.So,we carried out the PA experiment in spinor BEC.Through PA spectrums,we found possible regulatory sites and discussed the feasibility of controlling the magnetic properties of the system.The power of the PA laser would induce the shift and the broadening of the spectral,which would affect the position of scattering channels and the preparation of the corresponding molecular state.We constructed a theoretical model based on Feshbach resonance and experimentally verified the laser-induced frequency shift and spectral broadening in the spinor BEC.At extremely high PA laser intensities,we discovered the influence of the second-order Stark effect on the laser-induced frequency shift and accurately measured the second-order coefficient.It provides an experimental basis for the prediction and analysis of the Stark effect under high AC field,helps to further improve the accuracy of the study of important molecular properties and the preparation of specific molecular states.