1. Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck, Austria
2. Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria
3. RRC “Kurchatov Institute”,
Kurchatov Square 1, 123182, Moscow, Russia
4. Dipartimento di Fisica dell’Università
di Bologna, via Irnerio 46, 40126 Bologna, Italy
5. ISIS (UMR 7006) and IPCMS (UMR
7504), Université de Strasbourg and CNRS, Strasbourg, France