Many-electron effects of strong-field ionization described in an exact one-electron theory

TL;DR

This paper demonstrates that many-electron effects in strong-field ionization can be effectively modeled using a one-electron framework with the Exact Electron Factorization, highlighting the importance of time-dependent potentials and approximations for accurate simulations.

Contribution

It introduces a formalism using the Exact Electron Factorization to incorporate many-electron effects into a one-electron model for strong-field ionization, emphasizing the role of time-dependent potentials.

Findings

TICA approximation reproduces exact dynamics at high photon frequencies.

Time-dependent ionization barriers are crucial at lower frequencies.

Multi-state extensions of TICA can improve modeling of core dynamics.

Abstract

If one-electron observables of a many-electron system are of interest, a many-electron dynamics can be represented exactly by a one-electron dynamics with effective potentials. The formalism for this reduction is provided by the Exact Electron Factorization (EEF). We study the time-dependent features of the EEF effective potentials for a model of an atom ionized by an ultrastrong and ultrashort laser pulse, with the aim of understanding what is needed to develop computationally feasible approximations. It is found that the simplest approximation, the so-called time-independent conditional amplitude (TICA) approximation, is complementary to single-active electron (SAE) approaches as it reproduced the exact dynamics well for high photon frequencies of the laser field or large Keldysh parameter. For relatively low frequencies of the laser field or for smaller Keldysh parameters, we find that excited state dynamics in the core region of the atom leads to a time-dependent ionization barrier in the EEF potential. The time-dependence of the barrier needs to be described accurately to correctly model many-electron effects, and we conclude that a multi-state extension of the TICA approximation is a possible route how this can be achieved. In general, our study sheds a different light on one-electron pictures of strong-field ionization and shows that many-electron effects for such processes may be included by solving a one-electron Schr\"odinger equation, provided the core dynamics can be modeled successfully.