Atoms’ dipole moment controls collective quantum motion

Researchers from Harvard University and the Massachusetts Institute of Technology have demonstrated a surprising form of collective motion where pairs of atoms can move even when individual atoms are held immobile. The team realized a dipole-conserving Bose-Hubbard model using ultracold bosonic atoms in an optical lattice, effectively constraining particle movement while allowing pairs to move cooperatively and preserve the system’s overall dipole moment. This work provides a bottom-up investigation of a Hamiltonian with kinetic constraints and allows for the exploration of low-energy phases of fractonic matter. In many-body systems, limiting the mobility of individual particles can fundamentally alter the nature of collective dynamics. Localized excitations consisting of a hole and a doublon were generated within a one-dimensional chain of ultracold bosonic atoms, enabling the observation of constrained quantum dynamics. The research team used site-resolved optical potentials to create these excitations and subsequently characterize their quantum walks and scattering dynamics, revealing strongly-correlated multi-particle behavior. A strong linear potential effectively suppresses single-particle motion, leading to the conservation of…