1. Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria.
2. Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences A-6020 Innsbruck, Austria.
3. Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, A-1090 Vienna, Austria.
4. Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, A-1090 Vienna, Austria.
5. Photonics Laboratory, ETH Zürich, 8093 Zürich, Switzerland.
6. Quantum Center, ETH Zürich, 8093 Zürich, Switzerland.
7. Nanophotonic Systems Laboratory, Department of Mechanical and Process Engineering, ETH Zürich, 8092 Zürich, Switzerland.