1. Department of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands, Lash Miller Chemical Laboratories, 80 St. George Street, the Institute for Optical Sciences and Centre for Quantum Information and Quantum Control, University of Toronto, Ontario, M5S 3H6 Canada, and School of Physics and Centre for Immunology, The University of New South Wales, Sydney, N.S.W. 2052, Australia