1. IBM Research − Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
2. Department
of Physics, University of Basel, Klingbergstrasse 82, 4056 Basel, Switzerland
3. PRESTO, Japan Science and Technology Agency, Klingelbergstrasse 82, 4056 Basel, Switzerland
4. Department
of Applied Chemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700-0005, Japan
5. Institute
of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany