Reduced density matrix description of high-harmonic generation in multi-electron atoms: exploring sub-cycle correlation effects

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Hauptverfasser: Buczolich, Katharina, Sato, Takeshi, Ishikawa, Kenichi L., Lackner, Fabian, Burgdörfer, Joachim, Březinová, Iva
Format: Preprint
Veröffentlicht: 2025
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author Buczolich, Katharina
Sato, Takeshi
Ishikawa, Kenichi L.
Lackner, Fabian
Burgdörfer, Joachim
Březinová, Iva
author_facet Buczolich, Katharina
Sato, Takeshi
Ishikawa, Kenichi L.
Lackner, Fabian
Burgdörfer, Joachim
Březinová, Iva
contents High-harmonic generation (HHG) is one of the fundamental processes at the heart of attosecond physics. Traditionally viewed as an effective single-particle effect, recent advances have focused on contributions beyond this single-particle picture to the harmonic spectrum, as well as on probing electron correlations through HHG in atoms, molecules, and solids. In this paper, we introduce a reduced density matrix description to explore and to quantify correlation effects on a sub-cycle time scale and apply this approach to prototypical multi-electron atoms. By comparing noble gas atoms (He, Ne) with alkaline earth atoms (Be, Mg) exposed to driving fields with similar Keldysh parameters, we show that the sub-cycle variation of correlation parameters differs markedly for noble gases and alkaline earth atoms. We provide an intuitive explanation of these surprising effects based on the dynamics of natural orbitals and discuss the effect of this ultrafast correlation dynamics on the HHG spectrum.
format Preprint
id arxiv_https___arxiv_org_abs_2509_04869
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Reduced density matrix description of high-harmonic generation in multi-electron atoms: exploring sub-cycle correlation effects
Buczolich, Katharina
Sato, Takeshi
Ishikawa, Kenichi L.
Lackner, Fabian
Burgdörfer, Joachim
Březinová, Iva
Atomic Physics
Quantum Physics
High-harmonic generation (HHG) is one of the fundamental processes at the heart of attosecond physics. Traditionally viewed as an effective single-particle effect, recent advances have focused on contributions beyond this single-particle picture to the harmonic spectrum, as well as on probing electron correlations through HHG in atoms, molecules, and solids. In this paper, we introduce a reduced density matrix description to explore and to quantify correlation effects on a sub-cycle time scale and apply this approach to prototypical multi-electron atoms. By comparing noble gas atoms (He, Ne) with alkaline earth atoms (Be, Mg) exposed to driving fields with similar Keldysh parameters, we show that the sub-cycle variation of correlation parameters differs markedly for noble gases and alkaline earth atoms. We provide an intuitive explanation of these surprising effects based on the dynamics of natural orbitals and discuss the effect of this ultrafast correlation dynamics on the HHG spectrum.
title Reduced density matrix description of high-harmonic generation in multi-electron atoms: exploring sub-cycle correlation effects
topic Atomic Physics
Quantum Physics
url https://arxiv.org/abs/2509.04869