1. Université Grenoble Alpes and CEA,
INAC, F-38000 Grenoble, France
2. CEA-LETI, Minatec Campus, F-38054 Grenoble, France
3. Laboratory
for Micro- and Nanotechnology (LMN), Paul Scherrer Institut, CH-5232 Villigen, Switzerland
4. Institute
for Quantum Electronics, ETH Zurich, CH-8093 Zurich, Switzerland