1. Max Planck Institute for Nuclear Physics, Saupfercheckweg 1, Heidelberg 69117, Germany
2. Institute for Molecules and Materials, Radboud University, Heyendaalsweg 135, Nijmegen 6526 AJ, The Netherlands
3. Institute for Quantum Electronics, ETH Zürich, Auguste-Piccard-Hof 1, Zürich 8093, Switzerland