Quantum caging in interacting many-body all-bands-flat lattices

We consider translationally invariant tight-binding all-bands-flat networks which lack dispersion. In a recent work [C. Danieli et al., Phys. Rev. B 104, 085131 (2021)], we identified the subset of these networks that shows nonlinear caging in the presence of Kerr-like local nonlinearities, i.e., it preserves nonexcited network sites and therefore keeps compact excitations compact. Here we replace nonlinear terms by Bose-Hubbard interactions and study quantum caging. We identify the quantum caging conditions that are related to the nonlinear caging conditions and that guarantee the existence of an extensive set of conserved quantities in any lattice dimension, as first revealed in Tovmasyan et al. [Phys. Rev. B 98, 134513 (2018)] for a set of specific networks. Consequently, transport is realized through moving pairs of interacting particles that break the single-particle caging. We further prove the existence of degenerate energy renormalized compact states for any finite number 𝑀 of participating particles in one- and higher-dimensional lattice—results that explain and generalize previous observations for two particles on a diamond chain [Vidal et al., Phys. Rev. Lett. 85, 3906 (2000)].