1. IQMT, Karlsruhe Institute of Technology 1 , 76131 Karlsruhe, Germany
2. Departments of Applied Physics and Physics, Yale University 2 , New Haven, Connecticut 06511, USA
3. Yale Quantum Institute, Yale University 3 , New Haven, Connecticut 06511, USA
4. PHI, Karlsruhe Institute of Technology 4 , 76131 Karlsruhe, Germany
5. Physics Institute 1, Stuttgart University 5 , 70569 Stuttgart, Germany