1. Department of Materials Science and Engineering, Monash University, Melbourne 3800, Australia
2. ARC Centre of Excellence in Exciton Science, Monash University, Melbourne 3800, Australia
3. School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra 2601, Australia
4. Centre for Quantum Computation and Communication Technology, School of Engineering, Australian National University, Canberra 2601, Australia