Berlin 2015 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 69: Other Low Temperature Topics: Cold Atomic Gases
TT 69.5: Vortrag
Mittwoch, 18. März 2015, 16:00–16:15, A 053
Non-Equilibrium Expansion Dynamics in the 2D Bose-Hubbard Model — Mauricio Trujillo-Martinez1, •Anna Posazhennikova2, and Johann Kroha1 — 1Universität Bonn — 2Royal Holloway University of London, UK
We study the temporal expansion of an ultracold Bose gas in the 2D Bose-Hubbard model, where initially all bosons are put in one central site of the lattice. The time evolution of interacting many-body systems in more than one dimension has been a challenge for numerically exact methods. We therefore use the recently developed semianalytical method for time evolution of Bose systems [1] where the many-body Hamiltonian is represented in an appropriate, local eigenbasis and the corresponding field operators are separated into classical (BEC) and quantum mechanical parts. As consequence, the classical Gross-Pitaevskii BEC dynamics is coupled to the quantum fluctuations. After a quench, i.e. after a sudden switch of the lattice nearest neighbor hopping, the bosons spead over the lattice in a nontrivial way. The low-density part at the rim of the bosonic cloud spreads ballistically, while the spread of the high-density part in the center of the cloud is inhibited by interaction-induced self-trapping effects, characteristic for lattice dynamics. As a result, the bosonic cloud separates spatially into a ballisic fore-runner and a nearly self-trapped central part. The expansion velocity of the fore-runner is consistent with the Lieb-Robinson limit.
[1] M. Trujillo-Martinez, A. Posazhennikova, J. Kroha,
Phys. Rev. Lett. 103, 105302 (2009);
New J. Phys. in press; arXiv:1406.5536v2.