Macroscopic quantum self-trapping is a nonlinear regime of a bosonic Josephson junction in which an initial population imbalance does not undergo the full sign-changing tunneling oscillations expected from a simple linear two-state model. Interactions alter the relation between relative phase and population flow.
An experiment with two weakly linked condensates in a double-well potential measured both the density distribution and the relative phase inferred from interference fringes. Their combination distinguished nonlinear self-trapping from merely observing unequal populations at one instant.[ref]
