Anisotropic interactions of a single spin and dark-spin spectroscopy in diamond

Experiments on single nitrogen-vacancy (N-V) centres in diamond, which include electron spin resonance(1), Rabi oscillations(2), single-shot spin readout(3) and two-qubit operations with a nearby C-13 nuclear spin(4), show the potential of this spin system for solid-state quantum information processing. Moreover, N-V centre ensembles can have spin-coherence times exceeding 50 mu s at room temperature(5). We have developed an angle-resolved magneto-photoluminescence microscope apparatus to investigate the anisotropic electron-spin interactions of single N-V centres at room temperature. We observe negative peaks in the photoluminescence as a function of both magnetic-field magnitude and angle that are explained by coherent spin precession and anisotropic relaxation at spin-level anti-crossings. In addition, precise field alignment unmasks the resonant coupling to neighbouring 'dark' nitrogen spins, otherwise undetected by photoluminescence. These results demonstrate the capability of our spectroscopic technique for measuring small numbers of dark spins by means of a single bright spin under ambient conditions.