|M.Sc Student||Lahoud Elias|
|Subject||Thermal Damping of Macroscopic Quantum Self-Trapping in|
|Department||Department of Physics||Supervisor||Professor Jeff Steinhauer|
|Full Thesis text|
The experimental realization of a Bose-Einstein condensate in an ultra-high resolution system, has allowed for the creation of a single Josephson junction and the in-situ study of its dynamics. In this thesis we investigate the thermal damping of Macroscopic Quantum Self-Trapping (MQST). The MQST effect emerges under certain conditions in an atomic Josephson junction, and has a strong connection to the a.c. Josephson effect. The presence of the thermal cloud alongside the condensate is seen to cause the damping of this effect. This is manifest in the addition of an Ohmic resistance term to the Josephson equations, similar to the resistivity shunted Josephson junction in superconductors. The effect of the thermal cloud is accounted for using a simple model for the crossing of normal atoms across the barrier through thermal hopping, which is mostly driven by the chemical potential difference of the condensate fraction. The resulting population change in the normal atoms contributes to the chemical potential difference and drives the phase evolution of the condensates. In this work we have made direct measurements of the damping of MQST, taking multiple images of a single realization of a condensate using a nondestructive phase-contrast imaging technique. The ability to control the final temperature of the cloud has also allowed us to control the thermal fraction and hence the damping rate of MQST.