In this work, we study many-body excitations of Bose-Einstein condensates trapped in periodic one-dimensional optical lattices. In particular, we investigate the impact of quantum depletion onto the structure of the low-energy spectrum and contrast the findings to the mean-field predictions of the Bogoliubov-de Gennes (BdG) equations. Accurate results for the many-body excited states are obtained by applying a linear-response theory atop the multiconfigurational time-dependent Hartree method for bosons equations of motion. We demonstrate for condensates in a triple well that even weak ground-state depletion of around 1% leads to visible many-body effects in the low-energy spectrum, which deviates substantially from the corresponding BdG spectrum. We further show that these effects also appear in larger systems with more lattice sites and particles, indicating the general necessity of a full many-body treatment.
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© 2017 American Physical Society.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics