Relativistic Quantum Dynamics

Professor Fritzsche is a board member at the Helmholtz Institute Jena and head of the Theory Group at this institute. Prof. Fritzsche also serves as Principal Editor for Computer Physics Communications, a peer-reviewed international journal with focus on the numerical analysis and software design in physics and physical chemistry.

With the advent of new and tunable light sources, the electron dynamics of atoms and ions can nowadays be studied in great detail, from the femtosecond down to the attosecond scale. For instance, the irradiation of matter with intense FEL pulses hereby results in a large number of induced ionization, auto-ionization and recombination processes. To explore these - explicitly time-dependent - processes, we apply the density matrix theory to the emission and capture of electrons, and which combines analytical model with often extensive computations in order to achieve a quantitative (and predictive) understanding of light-matter interactions in strong fields. Beside of such atomic processes, we also investigate twisted particle beams carrying quantized angular momentum and the properties of highly-charged ions for their application in astro, nuclear and plasma physics.

Research Area

Prof. Fritzsche’s research interests deal with the structure and dynamics of finite quantum systems for applications in atomic and optical physics. Current research topics are: 

• Multi-photon ionization dynamics in intense FEL radiation
• Excitation, auto-ionization and decay cascades of atomic and molecular systems
• Light-matter interactions and light scattering in strong Coulomb fields
• Particle beams carrying quantized orbital angular momentum
• design and implementation of community tools for atomic, astro and plasma physics

Teaching Field

Prof. Fritzsche´s teaching has as its focus the behavior of correlated quantum systems and includes courses in:

• Atomic structure and collision theory
• Light-matter interactions in strong and short pulses
• Computational quantum physics

Research Methods

Various concepts and theoretical techniques are applied by Prof. Fritzsche's group for studying the structure and light-matter coupling of finite quantum systems, including:

• Relativistic atomic & many-body theory
• Numerical simulation techniques and code development
• Time-independent and time-dependent density matrix theory
• Computer-algebraic techniques
• Concepts and protocols from quantum information theory and quantum state estimation

Recent Research Results

Current research continues to address the dynamics of atoms and ions in intense and structured light fields. Recent theoretical work on strong-field ionization has shown how nonlinear interference structures in photoelectron momentum distributions encode sub-cycle electron dynamics and phase information of few-cycle laser pulses [1]. These studies have recently been extended to two-color fields, where phase and amplitude modulations can be resolved directly in the angular distribution of emitted electrons [2].

A second focus is the interaction of atoms with structured light. In particular, the group investigates few-cycle twisted laser pulses carrying orbital angular momentum and their influence on photoelectron emission [3]. Structured vector beams are also explored for atomic sensing: calculations for optically polarized atomic vapors demonstrate how spatially varying polarization patterns can be used to determine the magnitude and direction of external magnetic fields [4,5].

The group further develops relativistic atomic-structure and many-body tools for applications in highly charged ions, plasma physics and nuclear physics. Recent work includes electronic-bridge mechanisms for excitation of the low-lying nuclear isomer in ²²⁹Th [6] and the continued development of the Jena Atomic Calculator (JAC), which provides relativistic atomic data, transition amplitudes and cascade calculations for atoms and ions across the periodic table [7].

[1] Dar and Fritzsche, Phys. Rev. A 109, L041101 (2024).
[2] Dar et al., Phys. Rev. A 114, 023104 (2026).
[3] Dar et al., Phys. Rev. A 111, 053113 (2025).
[4] Ramakrishna and Fritzsche, Phys. Rev. A 111, 063110 (2025).
[5] Ramakrishna and Fritzsche, Phys. Rev. A 113, L031102 (2026).
[6] Wang et al., Phys. Rev. Lett. 133, 223001 (2024).
[7] Fritzsche et al., Plasma 9, 2 (2026).

Link to the Relativistic Quantum Dynamics GroupExternal link