1. Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom
2. Department of Physics, Universität Paderborn, Warburger Straße 100, 33098 Paderborn, Germany
3. Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, United Kingdom
4. Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
5. School Department of Physics and Astronomy and the Photon Science Institute, University of Manchester, Manchester M13 9PL, United Kingdom
6. Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark