The Magnetically Induced Feshbach Resonance In The Ultracold Alkali-metal Atomic Collisions And Its Modulation By Electric Field

This dissertation focuses on the magnetically induced Feshbach resonance in the ultracold alkali-metal atomic collision and its modulation by electric field. The main works are sum-marized as follows.(1)We developed the asymptotic-bound-state model to investigate the ultracold atomic collision in the presence of external electric and magnetic fields. The electric field modula-tion of Feshbach resonance, depending on the interatomic distance, can be simplified as a parameter, transition factor defined in our work. Using these parameters together with the binding energies of the least bound state, we calculated the Feshbach resonant position, width and thermal average scattering rate of6Li-40K in the presence of electric field. The results show that an electric field can modify the resonant positions and width. The width of the electric-field-induced s-wave resonance becomes narrow under the action of a strong electric field. The thermal average scattering rate constant can be changed by applying an electric field due to the variation of resonant width.(2)We demonstrated that the heteronuclear Feshbach resonance can be modified by the electric field component in radio-frequency (RF) field. The control mechanism is based on the interaction between RF electric field and the instantaneous dipole moment of the collision atomic pair. As an example, we investigated the RF field effect in the ultracold6Li-40K colli-sion, and found some interesting phenomena, such as the character exchange of the Feshbach resonances and resonance interference which results from the avoid crossing between different partial wave bound states.(3)Based on Lee-Yang binary collision theory, we derive the expressions for the virial coefficients up to the third order for two-species fermion mixtures, and investigate the fugac-ities of the species and the interaction energy density around the s-wave Feshbach resonance in6Li-40K mixtures. The theoretical results show that the magnitude of the virial coefficients depends on the mass ratio in a mass-imbalanced system. We found that the contribution of two-body bound states to high-order virial coefficients is very small at temperatures of microkelvin order. With the decrease of T/TF, the positions of the maxima of fugacity and interaction energy density shift away from the resonance position in the third-order virial expansion calculation. The mass ratio determines the relevance between the fugacity and number density of heavy species. Our conclusion is also effective for other mass-imbalanced systems.