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Q: Fachverband Quantenoptik und Photonik

Q 7: Quantengase: Bosonen im Gitter I

Q 7.4: Talk

Monday, March 2, 2009, 14:45–15:00, VMP 6 HS-A

Attractively bound pairs in the Bose-Hubbard model and anti-ferromagnetism — •Bernd Schmidt¹, Michael Bortz¹, Sebastian Eggert¹, David Petrosyan², and Michael Fleischhauer¹ — ¹Fachbereich Physik, Technische Universität Kaiserslautern, D-67663 Kaiserslautern, Germany — ²Institute of Electronic Structure & Laser, FORTH, 71110 Heraklion, Crete, Greece

We consider a periodic lattice loaded with pairs of bosonic atoms tightly bound to each other via a strong attractive on-site interaction that exceeds the inter-site tunneling rate. An ensemble of such lattice-dimers is accurately described by an effective Hamiltonian corresponding to the extended Hubbard model with strong repulsive interaction between the nearest neighbor sites corresponding to the anisotropic XXZ model. We calculate numerically and analytically the ground-state phase diagram for this system exhibiting incompressible phases, corresponding to an empty and a fully filled lattice (ferromagnetic phases) and a half-filled alternating density crystal (anti-ferromagnetic phase), separated from each other by compressible phases. In a 1D finite lattice the compressible phases show characteristic oscillatory modulations on top of the anti-ferromagnetic density profile and in density-density correlations. A kink model is derived which provides a simple and quantitative explanation of these features. The large-wavelength properties of the system can be described in terms of a Luttinger liquid.The relevant Luttinger parameter K is obtained exactly using the Bethe Ansatz. Density-density as well as first-order correlations are calculated and shown to be in excellent agreement with numerical results obtained with density matrix renormalization group methods.