1. Univ. Grenoble Alpes, CEA, IRIG-DEPHY, F-38000 Grenoble, France
2. Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
3. Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland
4. Univ. Grenoble Alpes, CEA, LETI, F-38000 Grenoble, France