  Ultracold dipolar particles pinned in optical lattices or tweezers provide an
excellent platform for studying out-of-equilibrium quantum magnetism with
dipole-mediated couplings. Starting with an initial state with spins of
opposite orientation in each of the legs of a ladder lattice, we show that spin
relaxation displays an unexpected dependence on inter-leg distance and dipole
orientation. This intricate dependence, stemming from the interplay between
intra- and inter-leg interactions, results in three distinct dynamical regimes:
(i) ergodic, characterized by the fast relaxation towards equilibrium of
correlated pairs of excitations generated at exponentially fast rates from the
initial state; (ii) metastable, in which the state is quasi-localized in the
initial state and only decays at exceedingly long timescales, resembling false
vacuum decay; and, surprisingly, (iii) partially-relaxed, with coexisting fast
partial relaxation and very long-lived partial quasi-localization. Realizing
these intriguing dynamics is within reach of current state-of-the-art
experiments in dipolar gases.
