Domain wall motion in an ultracold 87Rb gas

Synopsis

Spin diffusion in an ultracold nondegenerate bosonic gas is significantly affected by quantum collisions. In binary collisions of noncondensed indistinguishable particles, exchange symmetry can lead to a rotation of spins of the colliding particles. These spin-rotating collisions change dynamical properties of a multi-domain spin structure. Our magnetically-trapped two-level system is a quasi-one-dimensional pseudo-spin-12 gas of 87Rb atoms.

This thesis work studies motion of domain walls as spin diffusion takes place in a spin-dependent potential. To investigate domain wall motion, we devised a solution to optimally initialize the domains. We also developed an algorithm to analyze the experimental data to extract domain wall information.

The experimental results in this work suggest that the main prerequisite for the domain walls to move is asymmetry in the transverse spin distribution with respect to the wall center. The data shows that transverse spin distribution and total population ratio of the two states determine the type of motion a domain wall exhibits, and the path that it takes as the system evolves. Domain walls in the three-domain systems studied in this work exhibit a linear or oscillatory motion. To further understand domain wall motion, we also explored domain wall dynamics in two-domain systems. The results of this work are a first step in understanding why a domain wall moves, and how its trajectory can be controlled.