1 Department of Physics and IRIS Adlershof, Humboldt-Universität zu Berlin, 12489, Berlin, Germany.
2 Chair in Hybrid Nanosystems, Nanoinstitute Munich, Faculty of Physics, Ludwig-Maximilians-Universität München, 80539, Munich, Germany.
3 Department of Fiber Photonics, Leibniz Institute of Photonic Technology, 07745, Jena, Germany.
4 Department of Physics and IRIS Adlershof, Humboldt-Universität zu Berlin, 12489, Berlin, Germany. tim.kroh@physik.hu-berlin.de.
5 Competence Center for Micro- and Nanotechnologies, Leibniz Institute of Photonic Technology Jena, 07745, Jena, Germany.
6 Department of Physics, Imperial College London, London, SW7 2AZ, UK.
7 Physikalisches Institut and Center for Integrated Quantum Science and Technology, University of Stuttgart, Pfaffenwaldring 57, 70569, Stuttgart, Germany.
8 Otto Schott Institute of Material Research, 07743, Jena, Germany.