Defect-quasiparticle interactions

Defects in solid-state materials–e.g. the NV center in diamond, where a single nitrogen atom replaces a carbon atom, and the carbon atom right next to the nitrogen is vacant–may be the building block of scalable quantum computers. The goal is generally to decouple the defects from the surrounding host lattice as much as possible to prevent quantum information stored in the defects from leaking into the environment. As a result, interest has mostly been limited to defects in solid-state materials with wide band gaps so that defect orbitals within the band gap are far in energy from the electronic band edges and, thus, do not interact strongly with electronic band states and phonons. Not all interactions need be harmful, however–being able to interact with defects is necessary to load and extract quantum information from them, and perhaps the presence of one type of interaction could turn off another, more harmful interaction. I have three particular ideas in mind. The first is to study defects in materials with smaller band gaps, such as transition metal dichalcogenides, that also host excitons, or bound electron-hole pairs. How can we simulate such systems from first principles? Can we engineer a defect system to, say, force two excitons to interact through the defects or force two defects to interact through an exciton? The second is to understand what governs how strongly defects interact with host lattice phonons that are a leading cause of quantum information loss from defects. We can then design defects through first-principles simulations or group theoretical methods. The third idea is to study defects in magnetic materials that host magnons to couple defects together or isolate them from each other.