Title: Excited-State Dynamics and Optically Detected Magnetic Resonance of Solid-State Spin Defects from First Principles

Abstract: Optically detected magnetic resonance (ODMR) is an efficient and reliable method that enables initialization and readout of spin states through spin-photon interface. In general, high quantum efficiency and large spin-dependent photoluminescence (PL) contrast are desirable for reliable quantum information readout. However, reliable prediction of the ODMR contrast from first-principles requires 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 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 (NV) center in diamond. We show the importance of correct description of multi-reference electronic states for accurate prediction of excitation energy, spin-orbit coupling, and the rate of ISC. Moreover, we underscore the importance of pseudo Jahn-Teller effect for the spin-orbit coupling, and the dynamical Jahn-Teller effect for electron-phonon coupling, key factors determining ISC rates and ODMR contrast. 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 microwave frequency dependency, 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.