Many-body effects in a composite bosonic Josephson junction

Abstract: In standard bosonic Josephson junctions (BJJs), particles tunnel between two single-well potentials linked by a finite barrier. The dynamics of standard BJJs have been extensively studied, both at the many-body and mean-field levels of theory. In the present work, we introduce the concept of a composite BJJ. In a composite BJJ, particles tunnel between two double-well potentials linked by a finite potential barrier between them. We focus on many-body facets of quantum dynamics and investigate how the complex structure of the junction influences tunneling. Employing the multiconfigurational time-dependent Hartree for bosons method, highly-accurate many-boson wave-functions are obtained from which properties are computed. We analyze the dynamics using the survival probability, the degree of fragmentation of the junction, and the fluctuations of observables, and discuss how many-boson tunneling behaves, and how it may be controlled, using the composite nature of the junction. A central result of this work relates to the degree of fragmentation of composite BJJs with different numbers of bosons. We provide strong evidence that a universal degree of fragmentation into multiple time-dependent modes takes place. Further applications are briefly discussed.