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Q: Fachverband Quantenoptik und Photonik
Q 32: Quantengase (Gitter III)
Q 32.2: Talk
Thursday, March 13, 2008, 08:45–09:00, 1C
Direct Observation and Control of Superexchange Interactions with Ultracold Atoms in Optical Lattices — •Stefan Trotzky1, Patrick Cheinet1, Simon Fölling1,2, Michael Feld1,3, Ute Schnorrberger1, Ana Maria Rey4, Anatoli Polkovnikov5, Eugene Demler2,4, Mikhail Lukin2,4, and Immanuel Bloch1 — 1Johannes Gutenberg Universität Mainz — 2Harvard University, USA — 3Technische Universität Kaiserslautern — 4Harvard-Smithsonian Center of Astrophysics, USA — 5Boston University, USA
Quantum mechanical superexchange interactions form the basis of quantum magnetism in strongly correlated media. We report on the first direct observation of such superexchange processes with ultracold atoms in optical lattices. Our lattice set-up consists of a bichromatic superlattice along one spatial direction and two perpendicular monochromatic lattices, thus providing a three-dimensional array of double-wells. After preparing a spin-mixture of 87Rb atoms in an antiferromagnetic order along the superlattice axis, we record the spin dynamics within the double-wells. In the regime of strong interaction, coherent superexchange oscillations are observed which can be described by an effective Heisenberg Hamiltonian. We demonstrate, how the effective coupling parameter can be controlled in magnitude and sign, thus enabling the system to be switched between ferromagnetic or antiferromagnetic spin interactions. The experimental results show very good agreement with the predictions of a two-site Bose-Hubbard model, however, we are also able to identify corrections, which can be explained by the inclusion of direct nearest-neighbor interactions.