Excited-state spin coherence of a single nitrogen-vacancy centre in diamond

Nitrogen-vacancy centres in diamond are a solid-state analogue of trapped atoms, with fine structure in both the ground and excited states that may be used for advanced quantum control. These centres are promising candidates for spin-based quantum information processing1-3 and magnetometry4-6 at room temperature. Knowledge of the excited-state (ES) structure and coherence is critical to evaluating the ES as a room-temperature quantum resource, for example for a fast, optically gated swap operation with a nuclear-spin memory(7). Here we report experiments that probe the ES-spin coherence of single nitrogen-vacancy centres. Using a combination of pulsed-laser excitation and nanosecond-scale microwave manipulation, we observed ES Rabi oscillations, and multipulse resonant control enabled us to study coherent ES electron/nuclear-spin interactions. To understand these processes, we developed a finite-temperature theory of ES spin dynamics that also provides a pathway towards engineering longer ES spin coherence.