The excitation spectrum of a highly condensed two-dimensional trapped Bose-Einstein condensate (BEC) is investigated within the rotating frame of reference. The rotation is used to transfer high-lying excited states to the low-energy spectrum of the BEC. We employ many-body linear-response theory and show that, once the rotation leads to a quantized vortex in the ground state, already the low-energy part of the excitation spectrum shows substantial many-body effects beyond the realm of mean-field theory. We demonstrate numerically that the many-body effects grow with the vorticity of the ground state, meaning that the rotation enhances them even for very weak repulsion. Furthermore, we explore the impact of the number of bosons N in the condensate on a low-lying single-particle excitation, which is describable within mean-field theory. Our analysis shows deviations between the many-body and mean-field results which clearly persist when N is increased up to the experimentally relevant regime, typically ranging from several thousand up to a million bosons in size. Implications are briefly discussed.
Bibliographical noteFunding Information:
We thank Alexej I. Streltsov and Shachar Klaiman for many discussions. Computation time on the Cray XC40 cluster Hazel Hen at the High Performance Computing Center Stuttgart (HLRS) and the BwForCluster is acknowledged. R.B. acknowledges financial support by the IMPRS-QD (International Max Planck Research School for Quantum Dynamics), the Landesgraduiertenförderung Baden-Württemberg, and the Minerva Foundation. O.E.A. acknowledges funding by the Israel Science Foundation (Grant No. 600/15).
© 2018 American Physical Society.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics