  Inter-site dipolar interactions induce, even in absence of disorder, an
intriguing non-ergodic dynamics for dipolar bosons in an optical lattice. We
show that the inherent dipole-induced density-dependent tunneling, typically
neglected, plays a crucial role in this dynamics. For shallow-enough lattices,
the delocalization stemming from the interaction-induced hopping overcomes the
localization induced by inter-site interactions. As a result, in stark contrast
to the more studied case of hard-core bosons, delocalization is
counter-intuitively strengthen when the dipolar strength increases.
Furthermore, the quasi-cancellation between bare and interaction-induced
tunneling may lead, near a lattice-depth-dependent value of the dipole
strength, to an exact decoupling of the Hilbert space between ergodic hard-core
states and strongly non-ergodic soft-core ones. Our results show that
interaction-induced hopping should play a crucial role in future experiments on
the dynamics of polar lattice gases.
