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  • Letter
  • Open Access

Macroscopic quantum self-trapping in bosonic Josephson junctions: An exact quantum treatment

A. Bardin1,2,*, A. Minguzzi3, and L. Salasnich1,2,4

  • *Contact author: andrea.bardin.3@phd.unipd.it
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Phys. Rev. A 113, L031305 – Published 17 March, 2026

DOI: https://doi.org/10.1103/mzg8-gz84

Abstract

We investigate the fully quantum evolution of the population imbalance in a perfectly symmetric Bose-Josephson junction modeled by a two-mode Bose-Hubbard Hamiltonian, focusing on the validity of macroscopic quantum self-trapping beyond the mean-field theory. We show that for any finite number of particles, the exact quantum dynamics leads to the breakdown of macroscopic quantum self-trapping after a finite time, regardless of the initial state. Using the symmetries of the Bose-Hubbard Hamiltonian, we provide a mathematical demonstration of this result and analyze the spectral properties governing the dynamics. We identify a branching behavior in the eigenvalue differences and a nontrivial structure of the population-imbalance amplitudes. These features allow us to distinguish two clearly different dynamical regimes and to elucidate the mechanism leading to the emergence of a quasi–macroscopic quantum self-trapping regime for large particle numbers. These findings bridge the gap between mean-field predictions and exact quantum dynamics and provide insight into the emergence of classical nonlinear behavior from finite quantum many-body systems.

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Phys. Rev. A 113, L031305– Published 17 March, 2026
  • Received 6 August 2025
  • Accepted 23 February 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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