Laura Dreissen (Physikalisch-Technische Bundesanstalt)
: In an effort to formulate a quantum consistent theory of gravitation, it is suggested that Lorentz symmetry might be broken. We search for such an effects with precision spectroscopy of a trapped ytterbium ion in a Michelson-Morley type experiment. Rf spectroscopy in the meta-stable F-manifold enables a direct comparison of the orthogonally oriented atomic orbitals with coherence times of more than 1s. With this scheme, we have reached the highest sensitivity to date and have improved the bounds of the Lorentz symmetry breaking coefficients to the 10^-21 level. These results represent the best test of Lorentz symmetry in the electron-photon sector.