Near-Infrared-Assisted Charge Control and Spin Readout of the   Nitrogen-Vacancy Center in Diamond
  We utilize nonlinear absorption to design all-optical protocols that improve both charge state initialization and spin readout for the nitrogen-vacancy (NV) center in diamond. Non-monotonic variations in the equilibrium charge state as a function of visible and near-infrared (NIR) optical power are attributed to competing multiphoton absorption processes. In certain regimes, multicolor illumination enhances the steady-state population of the NV's negative charge state above 90%. At higher NIR intensities, selective ionization of the singlet manifold facilitates a protocol for spin-to-charge conversion that dramatically enhances the spin readout fidelity. We demonstrate a 6-fold increase in the signal-to-noise ratio for single-shot spin measurements and predict an orders-of-magnitude experimental speedup over traditional methods for emerging applications in magnetometry and quantum information science using NV spins. 
David A. Hopper, Richard R. Grote, Annemarie L. Exarhos, and Lee C.   Bassett
quant-ph cond-mat.mes-hall