Spectroscopy of Single N-V Centers in Diamond

Over the past few years, the detection of single N-V centers in diamond has attracted much interest, since it is expected to lead to innovative applications in various domains of quantum information. The N-V center in diamond is a defect consisting of a substitutional nitrogen atom adjacent to a carbon-atom vacancy. The optical transition between the A ground state and the E excited state has a very high quantum efficiency allowing single defect spectroscopy. Because of the paramagnetic nature of the ground electronic state, single N-V defects are believed to be promising candidates for solid state quantum computation. To date, however, the photophysics of the defect is not entirely understood. The existence of a singlet metastable state A was challenged in a series of papers reporting holeburning, optically detected magnetic resonance and single molecule experiments. We present here an overview of recent low and room temperature data, indicating the important role of a metastable state of the defect in single center experiments.