Far from equilibrium dynamics and quantum Kelvin-Helmholtz instability in a strongly ferromagnetic spinor condensate

The spinor Bose-Einstein condensate of atomic gases has a rich phase diagram and hosts various topological excitations, offering a new opportunity to study far-from-equilibrium dynamics and classify the universality class of nonequilibrium dynamics in quantum many-body systems. In this talk, I will introduce our recent experimental studies of nonequilibrium dynamics using spin-1 Bose gas of Lithium 7 atoms. We have studied the coarsening dynamics of the magnetic spin domains under two symmetries of the Hamiltonian: (1) easy-axis ferromagnetic regime with Z2 symmetry. (2) isotropic ferromagnetic regime with SO(3) symmetry. In each phase, we observe universal dynamic scaling of the domain coarsening, where the spin correlation functions at various hold times are collapsed into a single universal curve. Depending on the symmetry of the Hamiltonian, we find a distinctive scaling exponent that characterizes binary and diffusive fluids, respectively. In the second part of this talk, I will also introduce our recent experiment on the quantum Kelvin Helmholtz instability (KHI) of spin-1 superfluids. After preparing a single magnetic domain wall, we impose a counterflow by applying a magnetic field gradient. Thanks to our strong ferromagnetic spin interaction energy, it supports a sharp domain wall, which can be considered a vortex sheet. The flutter-finger pattern, the hallmark of the KHI, is observed on the magnetic domain boundary after 40 ms. In the nonlinear dynamic stage, a magnetic droplet is emitted from the tip of the finger, and further analysis shows that it has a fractional skyrmion charge with breaking axis symmetry.