1. School of Physics, University of Melbourne, Parkville, VIC 3010, Australia
2. Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Parkville, VIC 3010, Australia
3. Laser Physics Centre, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2601, Australia
4. National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
5. Melbourne Centre for Nanofabrication, Clayton, VIC 3168, Australia
6. Department Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2601, Australia