Interaction-driven interband tunneling of bosons in the triple well

We study the tunneling of a small ensemble of strongly repulsive bosons in a one-dimensional (1D) triple-well potential. The usual treatment within the single-band approximation suggests a suppression of tunneling in the strong-interaction regime. However, we show that several windows of enhanced tunneling are opened in this regime. This enhanced tunneling results from higher band contributions, and has the character of interband tunneling. It can give rise to various tunneling processes, such as single-boson tunneling and two-boson correlated tunneling of the ensemble of bosons, and is robust against deformations of the triple-well potential. We introduce a basis of generalized number states, including all contributing bands, to explain the interband tunneling, and demonstrate various processes of interband tunneling and its robustness by numerically exact calculation.