1. 3. Physikalisches Institute and Research Center SCOPE, University Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
2. National Institutes for Quantum and Radiological Science and Technology, Takasaki, Gunma 370-1292, Japan
3. Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden
4. Center for Quantum Information, Korea Institute of Science and Technology, Seoul 02792, South Korea