conditions using the NV− center in diamond Florian Dolde, ∗ Marcus W. Doherty, Julia Michl, Ingmar Jakobi, Boris Naydenov, Sebastien Pezzagna, Jan Meijer, Philipp Neumann, Fedor Jelezko, Neil B. Manson, and Jörg Wrachtrup 3. Physikalisches Institut, Research Center SCoPE and IQST, Universität Stuttgart, Pfaffenwaldring 57. D-70550 Stuttgart, Germany Laser Physics Centre, Research School of Physics and Engineering, Australian National University, Australian Capital Territory 0200, Australia Institut für Quantenoptik and IQST, Universität Ulm, Ulm D-89073, Germany Physikalisches Institut, Universität Leipzig, 04103 Leipzig, Germany