报告人：李铮研究员，北京大学
邀请人：段红光教授，李亮教授
报告时间：2025年6月17日（周二），14:30
报告地点：龙赛理科楼南楼401报告厅

报告人简介：
李铮，北大物理学院研究员，助理教授。主要从事第一性原理原子分子结构理论，分子动力学，自由电子激光，和光与物质相互作用领域的理论研究，着重于研究与自由电子激光相关的理论，在Science, Phys. Rev. Lett., Nature Comm., J. Am. Chem. Soc., Sci. Adv.等杂志发表研究论文七十余篇。

报告摘要：
The Jahn-Teller effect is a fundamental mechanism of spontaneous symmetry breaking in molecular and solid state systems, and has far-reaching consequences in many fields. Up to now, to directly image the onset of Jahn-Teller symmetry breaking remains unreached. Here we employ ultrafast ion-coincidence Coulomb explosion imaging with sub-10 fs resolution and unambiguously image the ultrafast dynamics of Jahn-Teller deformations of CH4+ cation in symmetry space. It is unraveled that the Jahn-Teller deformation from C3v to C2v geometries takes a characteristic time of 20+/-7 fs for this system. Classical and quantum molecular dynamics simulations agree well with the measurement, and reveal dynamics for the build-up of the C2v structure involving complex revival process of multiple vibrational pathways of the CH4+ cation. 
At the same time, we have proposed an analysis method for ultrafast diffraction imaging, which can be used to reconstruct the quantum state of molecular dynamics processes. And through external field control and quantum Zeno effect, we have achieved a selection of quantum states in the molecular dynamics process.

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