Dynamic polarization of single nuclear spins by optical pumping of NV   color centers in diamond at room temperature
  We report a versatile method to efficiently polarize single nuclear spins in diamond, which is based on optical pumping of a single NV color center and mediated by a level-anti crossing in its excited state. A nuclear spin polarization higher than 98% is achieved at room temperature for the 15N nuclear spin associated to the NV center, corresponding to $\mu$K effective nuclear spin temperature. We then show simultaneous deterministic initialization of two nuclear spins (13C and 15N) in close vicinity to a NV defect. Such robust control of nuclear spin states is a key ingredient for further scaling up of nuclear-spin based quantum registers in diamond. 
V. Jacques, P. Neumann, J. Beck, M. Markham, D. Twitchen, J. Meijer,   F. Kaiser, G. Balasubramanian, F. Jelezko and J. Wrac...