Marquis M. McMillan | Searcharxiv

arXiv2026

Spin Dynamics from Atomistic Quantum Simulations

Optically active solid-state spin defects are promising candidates for quantum applications, however a unified theoretical framework to predict their spin dynamics at high temperatures is not yet available. Here, using Kubo linear--response theory, we derive expressions of spin-lattice and decoherence times \(T_1\) and \(T_2\) in terms of correlation functions of spin--lattice couplings. We then evaluate \(T_1\) and \(T_2\) from molecular dynamics and spin--lattice interaction time--series generated by state--of--the--art machine learning models trained on {\it ab--initio} data. Finally we measure \(T_1\) times for the NV center in diamond and compare experimental and theoretical results, showing excellent agreement.

cond-mat.mtrl-sci↗

arXiv2025

First-Principles Framework for the Prediction of Intersystem Crossing Rates in Spin Defects: The Role of Electron Correlation

Optically active spin defects in solids are promising platforms for quantum technologies. Here, we present a first-principles framework to investigate intersystem crossing processes, which represent crucial steps in the optical spin-polarization cycle used to address spin defects. Considering the nitrogen-vacancy center in diamond as a case study, we demonstrate that our framework effectively captures electron correlation effects in the calculation of many-body electronic states and their spin-orbit coupling and electron-phonon interactions, while systematically addressing finite-size effects. We validate our predictions by carrying out measurements of fluorescence lifetimes, finding excellent agreement between theory and experiments. The framework presented here provides a versatile and robust tool for exploring the optical cycle of varied spin defects entirely from first principles.

cond-mat.mtrl-sci↗