## SCL Seminar by Martin Kuebler

Scientific Computing Laboratory seminar will be held on Thursday, 25 August 2016 at 14:00 in the library reading room “Dr. Dragan Popović" of the Institute of Physics Belgrade. The talk entitled

will be given by Martin Kuebler (Department of Physics, Technical University of Kaiserslautern, Germany).

Bosons in an optical lattice yield a paradigmatic quantum phase transition between a Mott insulator and a superfluid. Recently, a mean-field theory for the underlying Bose-Hubbard model has been developed, which allows to determine the location of this quantum phase transition quite accurately [1-3]. Here we extend the validity range of this mean-field theory with the help of a degenerate perturbation theory. This allows to study also harmonically confined optical lattices, where a wedding cake structure of insulating Mott shells with superfluid regions between the Mott shells emerges [4].

References:

[1] F. E. A. dos Santos and A. Pelster, Phys. Rev. A 79, 013614 (2009).

[2] B. Bradlyn, F. E. A. dos Santos, and A. Pelster, Phys. Rev. A 79, 013615 (2009).

[3] T. Wang, X.-F. Zhang, S. Eggert, and A. Pelster, Phys. Rev. A 87, 063615 (2013).

[4] K. Mitra, C. J. Williams, and C. A. R. Sa de Melo, Phys. Rev. A 77, 033607 (2008).

**"Improving mean-field theory for bosons in optical lattices via degenerate perturbation theory"**will be given by Martin Kuebler (Department of Physics, Technical University of Kaiserslautern, Germany).

**The abstract of the talk:**Bosons in an optical lattice yield a paradigmatic quantum phase transition between a Mott insulator and a superfluid. Recently, a mean-field theory for the underlying Bose-Hubbard model has been developed, which allows to determine the location of this quantum phase transition quite accurately [1-3]. Here we extend the validity range of this mean-field theory with the help of a degenerate perturbation theory. This allows to study also harmonically confined optical lattices, where a wedding cake structure of insulating Mott shells with superfluid regions between the Mott shells emerges [4].

References:

[1] F. E. A. dos Santos and A. Pelster, Phys. Rev. A 79, 013614 (2009).

[2] B. Bradlyn, F. E. A. dos Santos, and A. Pelster, Phys. Rev. A 79, 013615 (2009).

[3] T. Wang, X.-F. Zhang, S. Eggert, and A. Pelster, Phys. Rev. A 87, 063615 (2013).

[4] K. Mitra, C. J. Williams, and C. A. R. Sa de Melo, Phys. Rev. A 77, 033607 (2008).