1. Quantum Engineering Technology Labs, School of Physics and Department of Electrical and Electronic Engineering, University of Bristol, 5 Tyndall Ave., Bristol BS8 1FD, United Kingdom
2. School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, United Kingdom
3. EPSRC National Epitaxy Facility, Centre for Nanoscience and Technology, University of Sheffield, North Campus, Broad Lane, Sheffield S3 7HQ, United Kingdom