Liam P McGuinness1, Fedor Jelezko2. 1. Institute of Quantum Optics, Ulm University, Ulm, D-89069 Germany. School of Physics, University of Melbourne, Melboune, 3010 Australia. 2. Institute of Quantum Optics, Ulm University, Ulm, D-89069 Germany. Center for Integrated Quantum Science and Technology (IQST), Ulm University, Ulm, D-89069 Germany. fedor.jelezko@uni-ulm.de.