1. QuTech and Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft, The Netherlands
2. HRL Laboratories, 3011
Malibu Canyon Road, Malibu, California 90265, United States
3. Department
of Physics and Astronomy, and Station Q Purdue, School of Electrical
and Computer Engineering, School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, United States
4. Center
for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Copenhagen 1017, Denmark