1. FCT, Universidade do Algarve, Campus de Gambelas, 8005-117 Faro, Portugal
2. CQFM and IN, IST, Universidade Técnica de Lisboa, 1049-001 Lisboa, Portugal
3. Informatics and Electrotechnics, University of Rostock, 18055 Rostock, Germany
4. Institute of Physics, University of Rostock, 18055 Rostock, Germany