1. Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
2. Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, United Kingdom
3. Purdue University, West Lafayette, Indiana 47906, USA
4. Department of Physics and Astronomy, Interdisciplinary Nanoscience Center (iNANO), Aarhus University, 8000 Aarhus C, Denmark