Speaker
Description
Time-resolved spectroscopies provide direct access to observables that encode information about transient excited states and dynamical correlations in quantum materials. In this talk, I will present recent developments in efficient diagrammatic approaches for computing time-resolved spectral functions, centered on the Real-Time Dyson Expansion (RTDE), which reconstructs the time-nonlocal correlations through a perturbative expansion around nonequilibrium reduced density matrix trajectories while retaining the favorable scaling of single-time propagation schemes. I will discuss recent extensions of this framework to driven-dissipative systems, comparisons with the Kadanoff-Baym equations and the generalized Kadanoff-Baym ansatz. Further, I will comment on the role of self-consistency and Markovianity in describing transient spectral properties. Applications to photoexcited correlated semiconductors demonstrate the emergence of excitonic satellites, quasiparticle renormalization, and band-gap dynamics, illustrating how efficient NEGF methods can provide predictive simulations of modern ultrafast spectroscopic experiments.