State-selective intersystem crossing in nitrogen-vacancy centers

Motivated by recent measurements of state-selective intersystem crossing (ISC) in the nitrogen-vacancy (NV) center in diamond (see companion PRL), a new microscopic model is developed of the key ISC mechanism. These nonradiative transitions between states of different spin multiplicity are pivotal in the optical initialization and readout of the NV center's electronic spin, which has created a diverse range of room-temperature applications in metrology and quantum information science.