Theoretical Study On Photoassociation Of Ultracold Atoms,Feshbach Resonance Optimized Photoassociation

The formation and application of ultracold molecules is a hot topic in the field of atomic and molecular physics.As an effective method to prepare ultracold molecules,photoassociation has attracted wide attention of researchers,and the photoassociation of alkali-metal atoms is a very important part.The photoassociation of ultracold 133Cs atoms with shaped laser pulses and the Feshbach-optimized photoassociation of ultracold 39K and 133Cs atoms are studied theoretically by using the mapped Fourier grid method and the time-dependent quantum wavepacket method.The main work are summarized as follows:(1)We investigate theoretically the formation of ultracold Cs2 molecules via photoassociation(PA)with three kinds of pulses(the Gaussian pulse,the asymmetric shaped laser pulse SL1 with a large rising time and a small falling time and the asymmetric shaped laser pulse SL2 with a small rising time and a large falling time).For the three kinds of pulses,the final population on vibrational levels from v’=120～175 of the excited state displays a regular oscillation change with the pulse width and the interaction strength between colliding atom pair and pulse laser,and a high PA efficiency can be achieved with optimized parameters.The PA efficiency in the excited state steered by the SL1-pulse(SL2-pulse)train with optimized parameters which is composed of four SL1(SL2)pulses is 1.74 times as much as that by the single SL1(SL2)pulse due to the population accumulation effect.Moreover,a dump laser is employed to transfer the molecules from the excited state to the vibrational level v"=12 of the ground state to obtain stable molecules.(2)We investigate theoretically a Feshbach optimized photoassociation(FOPA)process for preparing ultracold excited-state 39K133Cs molecules.Under the joint action of magnetic field and short laser pulse,the colliding atoms in a scattering superposition state composed of eight hyperfine components are converted into a molecule in the vibrational level of the excited state via two transition processes,i.e.,the transition between singlet states and the transition between triplet states.The transition from a single hyperfine component to the excited target level is regarded as one transition path.Our calculation results show that there is the quantum interference effect between different transition paths in the FOPA process.The association efficiency can be significantly enhanced by taking advantage of Feshbach resonance.At different resonance positions,different hyperfine components of the superposition state dominate over the FOPA process,and the quantum interference displays different behaviors.Compared with the FOPA process only including a single hyperfine component,the quantum interference in the FOPA process containing all hyperfine components has a visible effect on the association efficiency.Moreover,the laser pulse peak intensity and the Boltzmann distribution have some influence on the FOPA efficiency and the quantum interference effect.