1. Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia.
2. Network for Computational Nanotechnology, Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907, USA.
3. Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Parkville, VIC 3010, Australia.