Excited-state dynamics and optically detected magnetic resonance of solid-state spin defects from first principles

Optically detected magnetic resonance (ODMR) is an efficient and reliable method that enables initialization and readout of spin states through the spin-photon interface. In general, high quantum efficiency and large spin-dependent photoluminescence contrast are desirable for reliable quantum information readout. However, reliable prediction of the ODMR contrast from first-principles requires an accurate description of complex spin polarization mechanisms of spin defects. These mechanisms often include multiple radiative and nonradiative processes, in particular, intersystem crossing (ISC) among multiple excited electronic states. In this work, we present our implementation of the first-principles ODMR contrast by solving the kinetic master equation with calculated rates from ab initio electronic structure methods then benchmark the implementation on the case of the negatively charged nitrogen vacancy center in diamond. We show the importance of the correct description of multireference electronic states and pseudo Jahn-Teller effect for quantitatively, even qualitatively correct prediction of spin-orbit coupling (SOC) and the rate of ISC. We present the complete calculation of SOC for different ISC processes that align with both group theory and experimental observations. Moreover, we provide a comprehensive picture of excitation and relaxation dynamics, including previously unexplored internal conversion processes. We show good agreement between our first-principles calculations and the experimental ODMR contrast under magnetic field. We then demonstrate reliable predictions of magnetic field direction, pump power, and Rabi frequency as important parameters for ODMR experiments. Our work clarifies the important excited-state relaxation mechanisms determining ODMR contrast and provides a predictive computational platform for spin polarization and optical readout of solid-state quantum defects from first principles.