1. Physics Department, Technical University of Munich, James-Franck-Str. 1, 85748 Garching, Germany
2. Institute for Advanced Study, Technical University of Munich, Lichtenbergstr. 2, 85748 Garching, Germany
3. Department of Mathematics, Vrije Universiteit Amsterdam, De Boelelaan 1111, Amsterdam, The Netherlands
4. Centre for Systems Dynamics and Control and Department of Mathematics, University of Exeter, Exeter EX4 4QF, United Kingdom