1. Center for Macroscopic Quantum States (bigQ), Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
2. Department of Electrical Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
3. Institute for Quantum Optics, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany
4. Felix Bloch Institute for Solid State Physics, University of Leipzig, 04103 Leipzig, Germany