Quantum-Geometric Light-Matter Interactions and Light-Induced Phases in Moiré Heterostructures

Irradiation with light provides a powerful tool to interrogate, control or induce new quantum states of matter out of equilibrium, however a microscopic understanding of light-matter coupling in interacting electron systems remains a profound challenge. Here, we show that THz radiation grants a new quantum-geometric handle to steer and probe correlated quantum materials, whereby light dynamically dresses the Wannier functions of interacting electrons which govern the low-energy dynamics, permitting a direct light-induced modulation of electronic interactions. Notably, this effect appears in any interacting electron system, but dominates optical properties in quantum materials with non-trivial quantum geometry or topology which host bands with poorly-localized or obstructed Wannier functions. We discuss ramifications for optical responses of twisted bilayer graphene and twisted transition-metal dichalcogenides and show that ultrafast THz pump-probe experiments provide a new avenue to explore the rich phase diagram of these materials and stabilize competing phases out of equilibrium.