Interacting Stark localization dynamics in a three-dimensional lattice Bose gas

We measure the thermalization dynamics of a lattice Bose gas that is Stark localized by parabolic potential. A non-equilibrium thermal density distribution created quickly removing an optical barrier. The resulting spatio-temporal are resolved using Mardia's $B$ statistic, which sensitive to shape entire distribution. conclude equilibrium achieved for all potential depths we sample, including strongly interacting and regime. However, slow non-exponential, requiring up 500 tunneling times. show Hubbard $U$ term not responsible via comparison exact diagonalization calculation, rule out equilibration driven lattice-light heating varying laser wavelength. timescale comparable next-nearest-neighbor time, suggests continuum, theory may be needed understand equlibration in this system.