1. Institute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of Sciences, Boltzmanngasse 3, 1090 Vienna, Austria
2. Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, 1020 Vienna, Austria
3. Institute of Computer Science, Masaryk University, 602 00 Brno, Czech Republic
4. Institute of Physics, Slovak Academy of Sciences, 845 11 Bratislava, Slovakia