In a quantum lattice model, turning up the interaction strength usually makes things happen faster — more energy, more dynamics, more complexity. The Bose-Hubbard model has been the standard testbed for this intuition: interactions between particles on a lattice drive phase transitions, create excitations, and generate correlations that spread through the system.
Maier and colleagues (arXiv:2602.20780) find the opposite. In a one-dimensional Bose-Hubbard chain initialized as a density-wave state, strong interactions suppress the spreading of correlations rather than enhancing them. The relaxation timescale grows inversely with interaction strength. Stronger interactions mean slower dynamics.
The mechanism: at strong coupling, the dynamics are dominated by doublon-holon pairs — tightly bound two-particle excitations that move as units. These composite objects are heavy. Their exchange generates domain-wall excitations, but the correlations from these excitations remain highly localized, decaying rapidly beyond nearest neighbors. The system maps exactly to an antiferromagnetic transverse-field Ising model, where the correlation propagation velocity is set by spin-wave excitations in the effective theory — and these spin waves slow down as the interaction strengthens.
Adding even a weak parabolic trap freezes the edge dynamics entirely. The boundaries, which normally participate in spreading correlations, become immobile. The suppression is double: strong interactions confine the dynamics to local doublon-holon exchange, and the trap further limits the spatial extent.
The general point: interaction strength is not synonymous with dynamical speed. When interactions bind particles into composite objects, the composite dynamics can be slower than the free-particle dynamics they replace. The system becomes more correlated locally and less correlated globally. Strength produces confinement, not chaos.