State-dependent phonon-limited spin relaxation of nitrogen-vacancy centers

Understanding the limits to the spin coherence of the nitrogen-vacancy (NV) center in diamond is vital to realizing the full potential of this quantum system. We show that relaxation on the vertical bar m(s) = -1 > <-> vertical bar m(s) = +1 > transition occurs approximately twice as fast as relaxation on the vertical bar m(s) = 0 <-> vertical bar m(s) = +/- 1 > transitions under ambient conditions in native NVs in high-purity bulk diamond. The rates we observe are independent of NV concentration over four orders of magnitude, indicating they are limited by spin-phonon interactions. We find that the maximum theoretically achievable coherence time for an NV at 295 K is limited to 6.8(2) ms. Finally, we present a theoretical analysis of our results that suggests Orbach-like relaxation from quasilocalized phonons or contributions due to higher-order terms in the spin-phonon Hamiltonian are the dominant mechanism behind vertical bar m(s) = -1 > <-> vertical bar m(s) = +1 > relaxation, motivating future measurements of the temperature dependence of this relaxation rate.

Automated summary

The study revealed that spin coherence in the native NV centers in high-purity bulk diamond is limited by spin-phonon interactions, with a maximum achievable coherence time of 6.8(2) ms at 295 K. The relaxation rate on specific transitions was found to be independent of NV concentration, indicating the dominant mechanism behind relaxation may be related to spin-phonon interactions. Future measurements of the temperature dependence of this relaxation rate are recommended.