January 28, 2026
Kai Li received his PhD in physics in 2023 under the mentorship of Linda Young, Professor in the Department of Physics, the James Franck Institute, and the College, as well as a Distinguished Fellow at Argonne National Laboratory. He is currently a postdoctoral researcher at JILA—a joint institute of The University of Colorado Boulder and the National Institute of Standards & Technology.
Li has been awarded the 2026 EuXFEL Young Scientist Award, which aims to recognize outstanding contributions to research at the European X-ray Free Electron Laser by young researchers in the early stages of their career. We interviewed him about his research and his time at UChicago.
Please explain the research for which you are being recognized with the 2026 EuXFEL Young Scientist Award.
The European XFEL produces extremely bright and ultrafast (~10-15 s) X-ray pulses that allow scientists to observe how atoms and molecules behave on their natural time and length scales. In my work, we used these pulses to perform X-ray stimulated Raman spectroscopy, a technique that probes electronic structure and dynamics. By carefully designing the experiment, we were able to improve the spectral resolution by nearly two orders of magnitude compared with previous approaches. This advance allows us to see much finer details in how matter responds to intense X-ray light, opening new possibilities for studying complex atomic and molecular dynamics.
What does this award mean to you?
This award is very meaningful to me both personally and professionally. It recognizes not only technical achievement but also creativity in using the unique capabilities of XFELs to push the limits of what is experimentally possible. It is especially rewarding to see that ideas first developed on paper ultimately worked so well in experiment. Receiving this award places me among a group of scientists who are helping shape the future of ultrafast X-ray science, which is both humbling and motivating.
What mentors, collaborators, or colleagues have had an impact on your work?
This work was carried out during my PhD at the University of Chicago under the supervision of Professor Linda Young. I am deeply grateful for her guidance, support, and encouragement to explore new ideas. I also benefited greatly from collaborations with many outstanding scientists from around the world and at the European XFEL, whose expertise and teamwork were essential to the success of the experiment.
Why did you choose UChicago?
I chose UChicago because of its strong tradition in fundamental physics research and its emphasis on deep understanding and intellectual independence. The opportunity to work with leading researchers in AMO (atomic, molecular, and optical) and X-ray science, as well as access to world-class experimental facilities, made it an ideal place for my doctoral studies. I also had the privilege of working with the AMO group at Argonne National Laboratory, where I utilized the world-leading Argonne Leadership Computing Facility and collaborated with internationally recognized scientists.
What was your primary area of study while at UChicago?
I pursued a PhD in physics with a focus on AMO physics. In particular, my research studied how intense X-ray free-electron laser pulses interact nonlinearly with dense gases, enabling new forms of X-ray spectroscopy.
Please describe your current job and your career path leading up to this point.
I am currently a postdoctoral researcher at JILA, where my work focuses on precision spectroscopy using ultra-stable and coherent extreme-ultraviolet (XUV) light to study the low-energy nuclear transition in thorium-229 (²²⁹Th). This transition is a leading candidate for a next-generation nuclear clock, which could surpass atomic clocks in robustness against environmental disturbances and enable new tests of fundamental physics, including dark-matter searches.
After earning my PhD at UChicago and before joining JILA, I completed a postdoctoral appointment at Princeton University, where I investigated ultrafast energy transfer in strongly coupled light–matter (polaritonic) systems. Through this work, I came to appreciate the importance of high-precision measurement techniques, which motivated me to join JILA and apply these tools to advance XFEL-related science.
What support did you receive at UChicago that proved valuable to you?
The rigorous education and research environment at UChicago provided a strong foundation for my career as a scientist. I am especially grateful for the mentorship and support from Professor Linda Young, who consistently encouraged curiosity, independence, and persistence—qualities that continue to guide my work today.