1. Center for Nonlinear Phenomena and Complex Systems, Université Libre de Bruxelles, CP 231, Campus Plaine, B-1050 Brussels, Belgium.
2. Fakultät für Physik, Ludwig-Maximilians-Universität, Schellingstr. 4, 80799 München, Germany.
3. Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching, Germany.
4. Munich Center for Quantum Science and Technology (MCQST), Schellingstr. 4, D-80799 München Germany.
5. Department of Physics, Harvard University, Cambridge, MA 02138, USA.
6. Department of Physics, Technical University of Munich, 85748, Garching, Germany.