Work package leader: Dr Ekkehard Peik, PTB Other participants: CMI, NPL, UMK, VTT Single ion trap from PTB In most of the advanced optical clocks, the linewidth is limited either by the laser or by decoherence in the atoms. While the first issue will be addressed in WP1, this work package will explore the limitations imposed to coherent trapping times in optical lattices and ion traps and will strive to reduce them. The aim is to achieve sub-Hz resolution with full contrast (100% excitation probability on resonance). This combination has so far not been obtained with any optical clock. Studies will be made of the different types of perturbations that limit the coherent interaction time for atoms and ions. For the case of atoms in an optical lattice, one needs to consider collisions, parametric heating through the lattice potential and the scattering of photons from the lattice light. For single ions in a radio frequency trap, the main concern is heating from fluctuating electric fields. In both cases, decoherence of the internal state due to coupling to electric and magnetic field noise must be avoided.