Temperature Sensitivity of ¹⁴N-V and ¹⁵N-V Ground-State Manifolds

We measure electron- and nuclear-spin transition frequencies in the ground state of nitrogen-vacancy (N-V) centers in diamond for two nitrogen isotopes (¹⁴N-V and ¹⁵N-V) over temperatures ranging from 77 to 400 K. Measurements are performed using Ramsey interferometry and direct optical readout of the nuclear and electron spins. We extract coupling parameters Q (for ¹⁴N-V), D, A_‖, A_⊥, and $$, and their temperature dependences for both isotopes. The temperature dependences of the nuclear-spin transitions within the $$ spin manifold near room temperature are found to be 0.52(1) ppm/K for ¹⁴N-V(|m = -1⟩ ↔ |m = +1⟩) and -1.1(1) ppm/K for ¹⁵N-V(|m = -1/2⟩ ↔ |m = +1/2⟩). An isotopic shift in the zero-field splitting parameter D between ¹⁴N-V and ¹⁵N-V is measured to be ~ 120 kHz. Residual transverse magnetic fields are observed to shift the nuclear-spin transition frequencies, especially for ¹⁵N-V. We have precisely determined the set of parameters relevant for the development of nuclear-spin-based diamond quantum sensors with greatly reduced sensitivity to environmental factors.