Topological protection is a central mechanism for ensuring robust quantum transport, yet the traditional understanding based on integer topological invariants often fails to account for the behavior of interacting many-particle systems. We addressed this by developing a quantum theory for topological pumps of self-bound composite objects, using an effective lattice Hamiltonian to describe their center-of-mass motion. Our analysis identified a specific topological invariant that governs the transport of these clusters, showing that increasing interaction strength modifies the composite band structure. We found that these interactions drive transitions between phases with integer and fractional topological charges, allowing for precisely controlled rational transport steps. These findings demonstrate that forming and manipulating self-bound objects through interactions provides a versatile tool for controlling topological properties in quantum systems.
Julius Bohm, Hugo Gerlitz, Christina Jörg and Michael Fleischhauer
"Quantum Theory of Fractional Topological Pumping of Lattice Solitons"
Phys. Rev. X 16, 011038 (2026)
