1. Interuniversity Microelectronics Center (IMEC), Kapeldreef 75, 3001 Leuven, Belgium
2. Department of Physics and Astronomy, Quantum Solid-State Physics (QSP) Division, Katholieke Universiteit Leuven, Celestijnenlaan 200D Box 2414, 3001 Leuven, Belgium
3. Department of Electrical Engineering, ESAT-INSYS Division, Katholieke Universiteit Leuven, Kasteelpark Arenberg 10, 3001 Leuven, Belgium
4. Department of Physics, Universiteit Antwerpen, Groenenborgerlaan 171, 2020 Antwerp, Belgium