Dynamics of one-dimensional Bose-Josephson Junction in a Box Trap: From Coherent Oscillations to Many-Body Dephasing and Dynamical Freezing

Abstract

Understanding how coherent quantum dynamics give way to correlation-dominated behavior in low-dimensional systems remains a central challenge in quantum many-body physics. Here, we address this problem by investigating the interplay of interactions and initial population imbalance in a one-dimensional Bose-Josephson junction confined in a box trap. Using the multiconfigurational time-dependent Hartree method for bosons (MCTDHB), we identify distinct dynamical regimes governed by the interplay between coherence and correlation-induced fragmentation. In the weakly interacting regime, the system exhibits coherent Josephson oscillations, while strong initial imbalance leads to damping. At intermediate interaction strength, fixing the interaction and varying only the initial imbalance, we uncover a crossover in the dynamics: very small imbalances yield nearly pure, non-fragmented oscillations; moderate imbalances induce many-body dephasing with collapse-and-revival behavior; and large imbalances drive equilibration accompanied by strong fragmentation and saturation of many-body observables, including orbital entropy and participation ratio. In the strongly interacting regime, the system enters a dynamical freezing regime characterized by pronounced fragmentation, where the density develops well-separated, particle-resolved peaks and tunneling is strongly suppressed. These results establish a unified picture of how coherence, dephasing, equilibration, and dynamical freezing emerge and compete in one-dimensional Josephson dynamics.