Investigation into Heating and Hyperfine Loss Mechanisms in Magnetically Trapped Ultra-Cold Rubidium

This thesis describes our investigation into elastic collisions between an ultra-cold, magnetically trapped atom ensemble of rubidium-87 or rubidium-85, and background, room-temperature rubid-ium. We investigated two specific phenomena: low scattering angle elastic collisions that change the trapped ensemble energy distribution without resulting in immediate trap loss, or “heating col-lisions”, and the dependence of elastic collisional loss cross-sections on the hyperfine state of the trapped rubidium ensemble. A theoretical description of quantum scattering theory is given, along with how this theory can be utilized to calculate heating collision rates. A theoretical and technical description of our rubidium magnetic/magneto-optical trap follows, including descriptions of two new additions to the system: an RF coil and a Zeeman optical pumping system. We then describe the methods used to experimentally determine trap loss rates and the energy distribution in the trap. Our results show that the average rate of energy imparted to a trapped atom in our system is on the order of 1 µK per second. We also show that the Rb-Rb loss rate slope 〈σv 〉 is independent of hyperfine state, indicating that any loss dependency on hyperfine state rests with collisions with other species, or other forms of loss. Revision: ubcdiss.cls r26 i