Tunable domain wall motion in multi-domain spin structures in an ultracold ⁸⁷Rb gas

We study domain wall motion in a pseudo-spin-½ ultracold ⁸⁷Rb gas initialized in an ‘up-down-up’ configuration. We measure domain wall velocities for various initial domain conditions and qualitatively distinguish two regimes of wall motion. At short times, transverse spin is confined to the domain walls, slowing down domain walls dynamics via exchange collisions. Later, coherence in the domain wall decreases, and the velocity of the wall increases. By studying the effects of initial coherence and transverse phase gradients in the domain wall on the wall dynamics, we identify controlling parameters and demonstrate the tunability of domain wall trajectories. We find that asymmetry in the spatiotemporal evolutions of initially symmetric longitudinal magnetization is related to asymmetry in phase gradients in the transverse magnetization. Numerical solutions of a quantum Boltzmann equation agree well with the measured wall trajectories. We also present progress toward using machine learning algorithms to predict conditions that lead to target domain wall motions.