IMPACTS · Isolating Many-Particle Correlations in Time and Space

Electronic excitations are crucial in many fields of science and engineering. Time-resolved spectroscopy is widely used to detect dynamics of excited particles (electrons) and quasiparticles (e.g., excitons or plasmons). In the scheme of “femtochemistry” established since decades, one excitation is placed into the system by a pump pulse and its evolution observed by a time-delayed probe pulse. However, this does not resolve correlations between multiple excitations making it impossible to understand important quantum phenomena.We shall develop and apply new experimental methods to determine multi-particle correlations, based on isolating higher (than fourth) orders of perturbation theory systematically. We will separate these contributions without requiring a-priori models. With tailored femtosecond laser pulse sequences, we circumvent the stochastic nature of light–matter interaction even though we use only classical light and retrieve information from specific orders of a perturbative expansion, hitherto only accessible theoretically.We also consider that many materials are heterogeneous. Thus, we isolate multi-particle correlations in space by combining high nonlinear orders with fluorescence microscopy and photoemission electron microscopy. This enables us to avoid ensemble averaging and obtain information for specific domains down to the single-molecule limit.Our methods will be applied to determine exciton diffusion in organic materials, chiral excitonic couplings, plexciton–plexciton interactions, quantum coherence in multi-exciton generation, phonon–phonon couplings in quantum dots, and the role of dark states in correlated materials.We expect IMPACTS to change how complex systems are studied with ultrafast spectroscopy. Overcoming limitations of single-particle models, we seek a holistic picture of correlated dynamics, impacting our understanding and application of solar energy conversion, transport in functional materials, and quantum technologies.