Exploring Pressure and Temperature Effects on the NV-Center Zero-Phonon Line in Diamond

The optical transition known as the zero-phonon line (ZPL) in the nitrogen–vacancy center is central to photon coherence and spectral stability in diamond-based quantum systems. Its energy and fine structure are highly sensitive to external perturbations such as temperature, pressure, and strain, yet the combined influence of these factors remains incompletely understood. We investigate the evolution of the ZPL under low-temperature and high-pressure conditions, where both the spectral shift and orbital splitting become pronounced. Using an effective spin–orbit–strain Hamiltonian for the excited ³E state, we numerically explore how pressure modifies the manifold and how off-axis strain components lift orbital degeneracy.