Ab initio study of N2V color center in lonsdaleite/diamond dual structure: A two-site Hubbard model

The N₂V color center is a promising defect for quantum memory applications due to its complex electronic structure from strongly correlated open-shell orbitals. Accurately describing the many-body electronic states, especially the singlet and metastable triplet states, is essential for quantum memory. This work combines Density Functional Theory (DFT) with a two-site Hubbard model to study the N₂V center in lonsdaleite/diamond dual structures. The results revealed two possible arrangements of the N₂V center, each with Zero Phonon Line (ZPL) values near 2.44–2.45 eV. Hubbard parameter analysis indicates electron delocalization in the dual structure, resulting in a broader luminescence spectrum. Electron-phonon coupling analysis showed stronger coupling and a wider phonon energy range in the lonsdaleite/diamond dual structure than in cubic diamond. Theoretical calculations overestimated electron-phonon coupling, but both theory and experiment show that the N₂V center in cubic diamond is a better single-photon emitter than in the dual structure, in line with the Hubbard model's prediction of a broader spectrum for the dual structure.