Theoretical Study On The Preparation Of Ultracold Molecule By Photoassociation And Feshbach Resonance

The preparation and application of ultracold molecules are hot research topics in atomic,molecular and optical physics.The photoassociation is a common technique to prepare the ultracold molecule.This dissertation investigates the photoassociation of the ultracold atom,Feshbach resonance and preparation of the ultracold molecule by mainly using the mapped Fourier grid method and the Chebychev polynomial propagation method.The research work includes three parts.We investigate the thermally averaged photoassociation dynamics of 85Rb atoms controlled by the pure cubic pulse and the preparation of deeply bound groundstate CsYb molecule via magnetic Feshbach-optimized photoassociaiton,propose the full optical control scheme to prepare the CsYb molecule in the ground rovibrational state via the laser-assisted self-induced Feshbach resonance.The main work are summarized as follows.(1)The initial states of the thermally averaged photoassociation are a series of translational states of the ground electronic state,where the state density is given by the weight of the Boltzmann distribution.At the ultralow temperature,the thermally averaged effect leads to the decrease of the photoassociation probability.In contrast to the Gaussian pulse,we find that pure cubic pulse reduces the influence of the thermal averaged effect on the photoassociation probability.The population transfer of the initial states in the high-weight-factor region is obviously suppressed by the Gaussian pulse,while the suppression does not exist for the pure cubic pulse.The pure cubic pulse can induce the population aggregation effect on the resonant vibrational states and accumulation effect on the off-resonant vibrational states of the excited electronic state,thus the population probability controlled by the pure cubic pulse is much higher than that controlled by the Gaussian pulse.(2)The magnetic Feshbach-optimized photoassociation to prepare the CsYb molecule in the ground vibrational state of the ground electronic state is investigated.In the theoretical calculation,with considering the Zeeman and internuclear-distance-dependent hyperfine coupling potential,the calculation finds three s-wave magnetic Feshbach resonance of CsYb system.Near the resonance position,the short-range probability density of the colliding atomic pair is significantly enhanced,which is beneficial to improve the photoassociation probability to prepare the deeply-bound-state molecule.The photoassociation rate coefficient of the closed-channel component is much larger than that of the open-channel component.We compare three two-laser control schemes with a four-laser control scheme.After optimizing the intensity and detuning of laser pulses,the population of the ground vibrational |φv"=0>state of the ground electronic state obtained in the four-laser scheme is higher than that in two-laser schemes,reaches 10-1 order of magnitude.(3)The full optical control scheme to prepare the ultracold CsYb molecule in the ground rovibrational state via laser-assisted self-induced Feshbach resonance is proposed.The atomic pair is bound in a harmonic oscillator trap of the three-dimension optical lattice,and occupies the lowest trap |n=0>state of the optical trap.Through the interaction of the laser with the permanent dipole moment,the laser-assisted self-induced Feshbach resonance takes place between the resonant |j=1/2,lg=0,J=1/2,MJ,P=+1,vgFB>channel of the ground electronic state and the trap |j’=1/2,l’g=1,J’,M’J,P’=-1,n=0>channel.Applying a chirped pulse can achieve the adiabatical converting of the atom pair in the trap channel to the Feshbach molecule in the resonant channel.The following pump-dump technique can be used to prepare the ultracold molecule in the ground rovibrational |vg=0,lg=0>state,the population transfer probability reaches 16%.In addition,the adiabatic converting from the Feshbach molecule to the ground-rovibrational-state CsYb molecule in |jf=1/2,lg=0,Jf=1/2,MJf=1/2,vg=0>channel can be achieved by the stimulated-Raman-adiabatic-passage technique,the population transfer probability reaches 99%.