1. Department of Chemistry and Physics, La Trobe University, Bundoora, Victoria 3086, Australia
2. School of Physics, The University of Melbourne, Parkville, Victoria 3010, Australia
3. National Measurement Institute, Lindfield, New South Wales 2070, Australia
4. Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
5. Institute of Condensed Matter Physics, Universität Erlangen, Staudt-Str. 1, 91058 Erlangen, Germany
6. School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia