Measurement-Based Nuclear Spin Cooling in NV Centers

Interactions between the electronic spin of the NV center and nuclear spins in its environment are a main source for decoherence in this system. Cooling down the surrounding nuclei will improve the coherence properties of the center, and therefore is desirable for potential applications. We propose utilizing dark resonance spectroscopy to narrow down the nuclear spin state distribution. In this scheme, the nuclei undergo anomalous spin diffusion at a rate which is proportional to the amount of electronic excitation in the system. The detunings of the lasers which illuminate the center distinguish a nuclear dark state which becomes a trapping state in the diffusion process. We analyze the mechanisms which limit this cooling procedure and explore the resulting minimal resolvable linewidth. We hypothesize that NV centers, which interact strongly with just a few nuclear spins, are promising candidates for achieving optimal line narrowing.