1. Radboud University, Institute for Molecules and Materials, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
2. University of Maryland, Department of Physics, Joint Quantum Institute, College Park, Maryland 20742, United States of America
3. Johns Hopkins University, Department of Chemistry, Baltimore, Maryland 21218, United States of America
4. Université de Rennes, Institut de Physique de Rennes, 263 avenue du Général Leclerc, Rennes CEDEX 35042, France