Many-body localization in tilted and harmonic potentials

We discuss nonergodic dynamics of interacting spinless fermions in a tilted optical lattice as modeled by a XXZ spin chain in a magnetic (or electric) field changing linearly across the chain. The time dynamics is studied using exact propagation for small chains and matrix product state techniques for larger system sizes. We consider both the initial Néel separable state and the quantum quench scenario, in which the initial state may be significantly entangled. We show that the entanglement dynamics is significantly different in both cases. In the former a rapid initial growth is followed by a saturation for sufficiently large tilt F . In the latter case the dynamics seems to be dominated by pair tunneling, and the effective tunneling rate scales as 1 / F2. In the presence of an additional harmonic potential the imbalance is found to be entirely determined by a local effective tilt Floc; the entanglement entropy growth is modulated with frequency that follows 1/Floc2 scaling first, but at long time the dynamics is determined rather by the curvature of the harmonic potential. Only for large tilts or sufficiently large curvatures, corresponding to the deeply localized regime, do we find logarithmic entanglement growth for the Néel initial state. The same curvature determines the long-time imbalance for large F, which reveals strong revival phenomena associated with the manifold of equally spaced states, degenerate in the absence of the harmonic potential.