Study Of The Ultracold Ytterbium Photoassociation Spectroscopy

The PA spectroscopy (PAS) based on cold atoms is a powerful tool for the research of cold collisions, detection of the long-range molecular potential and creation of cold molecules. Particularly, the scattering length can be tuned by the photoassociation laser, which is the so-called optical Feshbach resonance. In the dissertation, experimental study of PAS on ytterbium(Yb) atoms is described. Yb, as an alkaline-earth-like atom, is characterized by simple hyperfine structure and narrow inter-combination transition. The PAS on Yb atoms is useful to explore the studies on precise measurement, quantum simulation and quantum computation.The key point of ultracold Yb PAS experiment is creating samples with high-densities as well as ultra-low temperatures. We carefully studied the technology of laser cooling, loading the far-off-resonance trap (FORT) and optical evaporative cooling. We have successfully observed the PA spectrum with high resolution. The principal jobs for this dissertation are summarized as follows:1. We have built a digital laser frequency control system, which significantly depresses the frequency jitters of two-stage cooling lasers (399nm and556nm) and allows us to achieve frequency stability levels of304kHz and200kHz, respectively. Hyperfine splitting and isotope shifts corresponding to1Soâ†'3P1transition are measured with an accuracy of100kHz.2. We have loaded Yb atoms from a magneto-optical trap (MOT) to a FORT. Typically, about106Yb atoms with temperature as low as20μK can be trapped in FORT.3. We have performed optical evaporative cooling in1D FORT and crossed FORT, and finally174Yb BEC is achieved. The maximum condensation ratio is about30%, the amount of condensed atoms is around4×104and the critical temperature is between524and644nK.4. We have observed the PA spectrum of174Yb around4μK near1So-3P1intercombination line in crossed-FORT. Eight resonant lines of the molecular vibration state are observed within a red detuning range of GHz. The life time of3P1state is inferred from the PA peaks having sub-MHz linewidth.