One of the grand challenges of materials research is to understand and control quantum degrees of freedom in order to discover new phenomena and design materials with useful electronic, optical, and quantum properties. Achieving this goal requires a microscopic understanding of how interacting electrons and their excitations respond to light, electric fields, lattice vibrations, and other external perturbations.

The Qiu Group develops first-principles theoretical and computational methods for describing excited-state and nonequilibrium phenomena in quantum materials. A central focus of our work is many-body perturbation theory, including the GW and the Bethe-Salpeter equation (GW-BSE) approaches, together with real-time Green’s-function approaches for describing interacting electrons, excitons, and their dynamics. We are particularly interested in developing methods that connect microscopic many-body physics directly to experimentally measurable quantities.

Our research explores how many-electron interactions and light–matter coupling give rise to excitons, collective electronic states, coherent dynamics, nonlinear optical response, and ultrafast phenomena. We study questions ranging from how excitons move, interact, and lose coherence, to how strongly driven materials can acquire transient properties that do not exist in equilibrium, and how collective excitonic phases may be detected through optical spectroscopy, electron energy loss spectroscopy (EELS), and photoemission.

We also develop machine-learning approaches for many-body electronic structure, with the goal of extending the accuracy of first-principles excited-state calculations to much larger materials spaces. By combining physics-based electronic-structure theory with data-driven models, we aim to enable the prediction and discovery of materials with targeted excited-state, optical, and quantum properties.

Our work spans fundamental theory, computational method development, and close collaboration with experiment. Applications include quantum materials, optoelectronics, quantum information and sensing, and energy-related materials.