Modeling Impurities for Quantum Information Science

Defects and impurities in solids play an essential role in an array of technologies, most recently garnering attention for quantum information science. Transition metals, in particular chromium, are a ubiquitous source of contamination in materials growth and may also be intentionally introduced. Perhaps the best-known example is chromium in Al₂O₃, colloquially referred to as ruby, which enabled the first solid-state lasers. Computational tools based on density functional theory have been invaluable for building understanding on the role of defects and dopants in semiconductors, but the complicated excited-state structure arising from the d-orbital manifold of transition metals poses a particular challenge. Here I will discuss our work on Cr in three technologically relevant materials, GaN, AlN, and Ga₂O₃. For this, we utilized hybrid density functional theory, explicitly taking into account the multideterminant nature of the excited states. Our calculations provide insight into the role of coordination and local environment on the level structure of the impurity. I will also discuss our work in designing novel quantum defects, such as a scandium-vacancy complex in AlN, and the lessons we learned about electron-phonon coupling in this system. Lastly, I will detail the latest developments in the treatment of electron-phonon coupling in defects and impurities.