# For high-precision bosonic Josephson junctions, many-body effects matter

## TL;DR

This paper investigates the many-body quantum dynamics of ultracold Bose gases in Josephson junctions, revealing significant deviations from mean-field models and identifying new dynamic regimes influenced by interaction strength.

## Contribution

It introduces a comprehensive many-body simulation approach to Josephson junctions, highlighting effects overlooked by traditional mean-field models and discovering new dynamic phenomena.

## Key findings

- Many-body effects cause localized dynamics and soliton formation.
- Deviations from Gross-Pitaevskii predictions increase with interaction strength.
- Identification of the Fock flashlight regime through correlation measures.

## Abstract

Typical treatments of superconducting or superfluid Josephson junctions rely on mean-field or two-mode models; we explore many-body dynamics of an isolated, ultracold, Bose-gas long Josephson junction using time-evolving block decimation simulations. We demonstrate that with increasing repulsive interaction strength, localized dynamics emerge that influence macroscopic condensate behavior and can lead to formation of solitons that directly oppose the symmetry of the junction. Initial state population and phase yield insight into dynamic tunneling regimes of a quasi one-dimensional double well potential, from Josephson oscillations to macroscopic self-trapping. Population imbalance simulations reveal substantial deviation of many-body dynamics from mean-field Gross-Pitaevskii predictions, particularly as the barrier height and interaction strength increase. In addition, the sudden approximation supports localized particle-hole formation after a diabatic quench, and correlation measures unveil a new dynamic regime: the Fock flashlight.