Controlling Nonadiabatic Transitions through Engineered Ultrafast Laser Fields at Conical Intersections

Abstract In this paper, we investigate the coherent control of nonadiabatic dynamics at a conical intersection (CI) using engineered ultrafast laser pulses. Within a model vibronic system, we tailor the pulse chirp and temporal profile and compute the resulting wave packet population and coherence dynamics using projections along the reaction coordinate. This approach allows us to resolve the detailed evolution of wave packets as they traverse the degeneracy region with a strong nonadiabatic coupling. By systematically varying pulse parameters, we demonstrate that both chirp and pulse duration modulate vibrational coherence and alter branching between competing pathways, leading to controlled changes in the quantum yield. The reported yield corresponds to the dynamical branching outcome following passage through the CI rather than the thermodynamic steady-state population of the open quantum system. Our results elucidate the dynamic mechanisms underlying pulse-shaped control near CIs and establish a general framework for manipulating ultrafast nonadiabatic processes.