Ultrafast X-ray spectroscopy of light-engineered quantum materials

Coherently engineering quantum states with light is a key frontier in controlling quantum materials. Over the last two decades, ultrafast lasers have revealed a variety of emergent topological, magnetic, and superconducting states in materials driven far from equilibrium. Early experiments mainly adopted incoherent excitation schemes, but more recently, mid-infrared and THz lasers have enabled coherent control of solids by directly manipulating quasi-classical collective modes and macroscopic order parameters. Future progress hinges on demonstrating deterministic, coherent control of quantum states, especially in systems governed by many-body interactions. In this talk, I will discuss examples of ultrafast engineering of microscopic Hamiltonians of prototypical many-body states. I will show how ultrafast lasers can amplify, suppress, or switch electronic interactions, and how ultrafast X-ray spectroscopy can quantify these modified Hamiltonian terms by interrogating driven electronic states at finite momentum. These capabilities pave the way for synthesizing arbitrary target Hamiltonians and long-lived electronic phases and establish a clear pathway to the rational design of novel quantum states of matter.