1. Optical Nanomaterial Group Institute for Quantum Electronics Department of Physics, ETH Zurich Auguste‐Piccard‐Hof 1 8093 Zurich Switzerland
2. Institute for Electronics Department of Information Technology and Electrical Engineering, ETH Zurich Gloriastrasse 35 8092 Zurich Switzerland
3. Institute for Electromagentic Fields Department of Information Technology and Electrical Engineering, ETH Zurich Gloriastrasse 35 8092 Zurich Switzerland
4. Soft Matter Physics Group Adolphe Merkle Institute University of Fribourg Chemin des Verdiers 4 1700 Fribourg Switzerland