Broad High-partial-wave Feshbach Resonances In Ultracold Atomic Gases

With clean models and versatile controllability,ultracold atomic gases have opened up unprecedented possibilities to study many-body systems dominated by strong interatomic interactions.Tremendous progresses have been made through the use of Feshbach resonance?FR?which can control the effective interactions between ultracold atoms.While low-loss broad s-wave FRs have found a wealth of applications in studying novel quantum few-and many-body phenomena,broad high-partial-wave FRs with small atom losses,on the other hand,remain to be found,although atom-ic gases near them are predicted to exhibit richer physics accompanied by quantum phases nonexistent with s-wave interactions.This thesis presents both experimental and theoretical studies for broad high-partial-wave FRs in ultracold atomic gases.An experimental apparatus for preparing an ultracold⁸⁵Rb-⁸⁷Rb mixture is constructed for investigating magnetic Feshbach res-onances at fields up to 1000 G.Capitalizing on this experimental system,we report the first observation of broad d-wave FRs as well as their characteristic triplet splitting structure induced by interatomic spin-spin interaction.These tunable broad d-wave resonances could find important applications in studying many-body systems with d-wave coupling.The aforementioned experimental work is stimulated and guided by an analytic multichannel quantum-defect theory?MQDT?,which is found to be robust and effi-cient for predicting and characterizing FRs of high partial waves.Based on this theory,I further calculate the splittings of p-and d-wave FRs and quantitatively compare them with experimental measurements.Three calculation methods are presented,including the MQDT assisted by perturbation theory,the MQDT assisted by Kohn variational principle,and the coupled-channel calculation.This work has improved the under-standings of how the spin-spin interaction affects ultracold collisions and FRs.Finally,a comprehensive investigation of broad high-partial-wave FRs in all sta-ble alkali-metal systems are carried out by analytic MQDT.Previously unknown broad s-,p-,and d-wave FRs are predicted in many alkali-metal systems,and a recently ob-served unique broad d-wave shape resonance in⁴¹K is identified and highlighted.We also find that broad p-or d-wave FRs free of two-body loss do not exist for all possible fermionic alkali-metal combinations.These results provide helpful guidance to exper-imental explorations of high-partial-wave coupling dominated many-body physics.