1. Radboud University, Institute for Molecules and Materials, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
2. Université de Rennes, Institut de Physique de Rennes, 263 avenue du Général Leclerc, Rennes 35042 CEDEX, France
3. University of Maryland, Department of Physics, Joint Quantum Institute, College Park, Maryland 20742, United States of America