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Inter-species Tunneling in One-dimensional Bose Mixtures

We study the ground-state properties and quantum dynamics of few-boson mixtures with strong inter-species repulsion in one-dimensional traps. If one species localizes at the center, e.g., due to a very large mass compared to the other component, it represents an effective barrier for the latter and the system can be mapped onto identical bosons in a double well. For weaker localization, the barrier atoms begin to respond to the light component, leading to an induced attraction between the mobile atoms that may even outweigh their bare intra-species repulsion. To explain the resulting effects, we derive an effective Hubbard model for the lighter species accounting for the backaction of the barrier in correction terms to the lattice parameters. Also the tunneling is drastically affected: Varying the degree of localization of the "barrier" atoms, the dynamics of intrinsically noninteracting bosons can change from Rabi oscillations to effective pair tunneling. For identical fermions (or fermionized bosons) this leads to the tunneling of attractively bound pairs.