Multiconfigurational nature of electron correlation within nitrogen vacancy centers in diamond

Diamond is a solid-state platform used to develop quantum technologies, but it has been a long-standing problem that the current understanding of quantum states of nitrogen vacancy (NV) centers in diamond is mostly limited to single-electron pictures. Here, we combine the full configuration interaction quantum Monte Carlo method and the density-matrix functional embedding theory to achieve an accurate description of the many-body quantum states of such defects in diamond. More than 30 electrons and 130 molecular orbitals are correlated, revealing the multiconfigurational nature of the wave functions of the many-body quantum states therein. Such a description explains puzzling experimental measurements in intersystem crossing and charge-state transitions at NV centers in diamond. The calculations not only reproduce the available experimental measurements of the energy gaps between quantum states but also provide benchmarks for states that are still subject to considerable uncertainty.