[1] Tech Univ Denmark, Dept Phys, DK-2800 Fysikvej, Kongens Lyngby, Denmark
[2] Ulm Univ, Inst Quantum Opt, Albert Einstein Allee 11, D-89081 Ulm, Germany
[3] Hebrew Univ Jerusalem, Racah Inst Phys, IL-91904 Jerusalem, Israel
[4] Ulm Univ, Ctr Integrated Quantum Sci & Technol IQst, D-89081 Ulm, Germany