1. Institute for Experimental and Applied Physics and Regensburg Center for Ultrafast Nanoscopy (RUN), University of Regensburg, 93040 Regensburg, Germany.
2. Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel.
3. Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany.
4. IBM Research–Zurich, 8803 Rüschlikon, Switzerland.