/en/research/projects/2.3/topics/Attosecond electron correlation/index.html
2.3 Time-resolved XUV-science
Project coordinator(s): A. Rouzée, S. Patchkovskii
Topic: Theory of attosecond multi-electron dynamics during XUV photoionization and its coupling to nuclear motion at the femtosecond timescale

Topic Goals

Our goal is to analyze attosecond dynamics of photo-ionization in atoms and molecules, from diatomic to polyatomics. One of the key novel issues is the dynamics of the hole created by ionization: where is it located after ionization, is it localized or not, how strong is the electron-hole entanglement, and therefore what is the degree of the hole coherence? To answer these questions, we are developing theoretical approaches for treating photo-ionization of atoms and molecules by attosecond pulses, with or without the presence of additional IR fields. The approaches include two complementary ab-initio methods: R-matrix and the adaptation of multiple configuration time-dependent Hartree method (MCTDH), originally designed for bosons, to fermions. Numerical methods are pursued in combination with semi-analytical approaches utilizing WKB approximation to describe the motion of the photo- electron in the presence of a strong IR field.

Present key activities

Attosecond dynamics of photo-ionization
M. Ivanov, O. Smirnova, A. Harvey, F. Morales Moreno

How long does it take an electron to become free after photo-activation (photon-absorption)? What are the physical mechanisms behind possible time delays, and what is the role of electron-electron correlation in it? To answer these questions, we are using both analytical and numerical techniques: the WKB approach to look at single-electron effects and the adaptation of multiple configuration time-dependent Hartree method (MCTDH) to fermions, to look at multi-electron effects.

Modeling electronic response of small and larger molecules to ultrafast excitations using R-matrix method
A. Harvey, F. Morales Moreno, O. Smirnova

The R-matrix method is a sophisticated, ab initio, fully quantum, method, originally developed for scattering problems and for stationary (time-independent) treatment. Our goal is to adapt it to photo-ionization of polyatomic molecules, with or without the presence of strong IR laser field that modifies the continuum dynamics, and to incorporate explicit time-dependence into the calculations. Recently, we have been able to obtain first results for photo-ionization amplitudes of aligned CO2 molecules, as a function of the angle between the molecular axis and the direction of the outgoing electron.

Interplay of attosecond electron coherence and femtosecond nuclear dynamics
L. Medisauskas, M. Ivanov, O. Smirnova, F. Morales Moreno

Ultrafast ionization can created coherent superposition of ionic states and launch a multi-electron wavepacket in the molecular ion. It is convenient to think about such wavepacket as the motion of the hole across the molecule. While the initial hole dynamics is determined entirely by the electronic structure and is attosecond, oscillations and transfer of the electron charge across the molecule could and usually will lead to femtosecond nuclear dynamics. Our theoretical efforts, in combination with parallel experimental work at MBI, are aimed at understanding the possible interplay between coherent electronic and nuclear motion, from attosecond to femtosecond time-scale.