Bose-Einstein condensation of Strontium-84
The achievement in 1995 of Bose-Einstein condensates (BEC) in dilute gases of alkali- metal atoms was one of the most important experimental results in recent times. Fifteen years later, the study of quantum fluids is a vibrant field exploring topics such as the effects of dimensionality and disorder on quantum fluids and the modeling of condensed-matter systems with BECs in optical lattices. This thesis describes the achievement of BEC in the alkaline-earth metal atom strontium (Sr). This new addition to the family of elements that have been Bose-condense opens new possibilities, such as the use of an optical Feshbach resonance to tune atom-atom interactions with relatively low atomic losses. Equally exciting theoretical proposals have been made for using quantum fluids made of alkaline-earth metal atoms, like creating exotic quantum magnetism states and demonstrating quantum computation in optical lattices. Previous efforts at achieving BEC with Sr focused on using the most abundant isotopes, 88Sr and 86Sr, without success. This thesis also describes our use of two-photon photoassociation spectroscopy (PAS) for accurate determination of the s-wave scattering length a (a measure of the interaction strength) for all the Sr isotopes and isotope mixtures. This result was essential for determining that bosonic 84Sr possesses the ideal collisional properties for efficient evaporative cooling to quantum degeneracy. 84Sr would not otherwise be the isotope of choice because its natural abundance is very low (0.6%). The PAS results also showed that 88Sr and 86Sr have unfavorable collision properties, which explains the difficulties encountered when attempting to form quantum degenerate 88Sr and 86Sr.
Atoms & subatomic particles;
0748: Atoms & subatomic particles