Bosonic Josephson junction

Two weakly linked Bose-Einstein condensates form a bosonic Josephson junction. Their relative phase controls a particle current through the weak link, analogous to the pair current of a superconducting Josephson junction. For neutral reservoirs the phase evolution follows a chemical-potential difference rather than an electric voltage. Interactions can make the tunneling dynamics nonlinear, including self-trapping at sufficiently large imbalance.

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]

Two weakly coupled condensates in a double-well potential realize one bosonic Josephson junction. The 2005 experiment measured the density distribution in situ and inferred the evolving relative phase from interference fringes. It distinguished tunneling oscillations from nonlinear suppression of large-amplitude transfer, called macroscopic quantum self-trapping.^[ref]