Quantum gases with tunable interactions in optical lattices and photoassociation of molecules in optical lattices

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We are planning to pursue two main experimental research goals within the second funding period of this "Schwerpunktprogramm". Building on our highly successful work on Bose-Einstein condensates in optical lattices, we will focus our work on the creation of a 85Rb condensate in an optical lattice potential. In 85Rb a broad Feshbach resonance would allow us to tune the scattering length of the atoms over a wide range and thereby have complete control over the interaction parameters between the atoms. We therefore would not only be able to tune the tunnel coupling between different lattice sites through the optical lattice potential depth, but also control the interaction parameter and thereby gain complete control over all parameters in the fundamental underlying Bose-Hubbard Hamiltonian. A controllable onsite interaction parameter would be very useful in order to study the Mott insulator phase transition by simply changing the interactions between the atoms and would also allow us to resolve many interaction related effects spectroscopically by having a higher and then more easily resolvable energy scale given by U. A second focus of our work will be directed towards the creation of ultracold molecules in optical lattices via coherent two-photon photoassociation processes. By filling lattice sites from a Mott insulator with two atoms one could induce a highly effective bound-bound photoassociation process to vibrational states in the triplet or singlet molecular ground state potential.