| Quantum transport has in 'conventional' lattices proven to be a powerful method for characterization of the band structure. Here we report on experiments studying the transport of atomic Bose-Einstein condensates in periodic potentials of variable symmetry. By monitoring the Landau-Zener effect and Bloch-oszillations, we have explored the band structure of both ratchet-type asymmetric and symmetric optical potentials. For a realization of lattice potentials with variable symmetry, a conventional lattice of lambda/2 spatial periodicity is superimposed with a fourth-order lattice potential of lambda/4 periodicity. The high periodicity lattice is realized using dispersive properties of multiphoton Raman transitions. In transport experiments we find that the Landau-Zener tunneling rate between the first and the second excited Bloch band depends critically on the relative phase between the two spatial lattice harmonics. Our experimental results are in agreement with theoretical calculations. |
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