title: Dark states of single nitrogen-vacancy centers in diamond unraveled by single shot NMR.
abstract: The nitrogen-vacancy (NV) center in diamond is supposed to be a building block for quantum computing and nanometer-scale metrology at ambient conditions. Therefore, precise knowledge of its quantum states is crucial. Here, we experimentally show that under usual operating conditions the NV exists in an equilibrium of two charge states [70% in the expected negative (NV-) and 30% in the neutral one (NV0)]. Projective quantum nondemolition measurement of the nitrogen nuclear spin enables the detection even of the additional, optically inactive state. The nuclear spin can be coherently driven also in NV0 (T1≈90  ms and T2≈6  μs).
authors.affiliation: 3. Physikalisches Institut and Research Center SCOPE, University of Stuttgart, 70569 Stuttgart, Germany. g.waldherr@physik.uni-stuttgart.de
authors.forename: G
authors.initials: G
authors.lastname: Waldherr
authors.forename: J
authors.initials: J
authors.lastname: Beck
authors.forename: M
authors.initials: M
authors.lastname: Steiner
authors.forename: P
authors.initials: P
authors.lastname: Neumann
authors.forename: A
authors.initials: A
authors.lastname: Gali
authors.forename: Th
authors.initials: T
authors.lastname: Frauenheim
authors.forename: F
authors.initials: F
authors.lastname: Jelezko
authors.forename: J
authors.initials: J
authors.lastname: Wrachtrup