1. Bogolyubov Institute for Theoretical Physics (BITP), Ukrainian National Academy of Sciences, 14-b, Metrologicheskaya Str., 03680 Kiev, Ukraine
2. Physikalisches Institut, University Heidelberg, Im Neuenheimer Feld 226, 69120 Heidelberg, Germany
3. Department of Atomic Physics, Eötvös University, Pázmány P. s. 1/A, H-1117 Budapest, Hungary
4. Wigner Research Centre for Physics, 114, P.O. Box 49, H-1525 Budapest, Hungary
5. MATE Institute of Technology, Károly Róbert Campus, Mátrai út 36, H-3200 Gyöngyös, Hungary