[1] Goethe Univ Frankfurt, Frankfurt Inst Adv Studies, D-60054 Frankfurt, Germany
[2] Goethe Univ Frankfurt, Frankfurt Int Grad Sch Sci, D-60054 Frankfurt, Germany
[3] Siemens AG, Corp Technol Informat & Commun, D-81730 Munich, Germany
[4] Univ Giessen, Inst Theoret Phys, Giessen, Germany