arXiv subjects

Petra Ruth Kaprálová-Žďánská

Publications and source records attributed to Petra Ruth Kaprálová-Žďánská.

4 recordsLinked to original sources

arXiv2021

Quasiclassical approach to quantum quench dynamics in the presence of an excited-state quantum phase transition

The dynamics of a quantum system following a sudden, highly non-adiabatic change of its control parameter (quantum quench) is studied with quasiclassical techniques. Recent works have shown, using exact quantum mechanical approach, that equilibration after quantum quench exhibits specific features in the presence of excited-state quantum phase transitions. In this paper, we demonstrate that these features can be understood from the classical evolution of the Wigner function in phase space.

quant-ph↗

arXiv2019

Ab-initio Theory of Photoionization via Resonances

We present an \emph{ab-initio} approach for computing the photoionization spectrum near autoionization resonances in multi-electron systems. While traditional (Hermitian) theories typically require computing the continuum states, which are difficult to obtain with high accuracy, our non-Hermitian approach requires only discrete bound and metastable states, which are accurately computed with advanced quantum chemistry tools. We derive a simple formula for the absorption lineshape near Fano resonances, which relates the asymmetry of the spectral peaks to the phase of the complex transition dipole moment. Additionally, we present a formula for the ionization spectrum of laser-driven targets and relate the `Autler-Townes' splitting of spectral lines to the existence of exceptional points in the Hamiltonian. We apply our formulas to compute the autoionization spectrum of helium, but our theory is also applicable for non-trivial multi-electron atoms and molecules.

physics.optics↗

arXiv2019

Optical absorption in atoms and molecules near laser-induced exceptional points

We present a non-Hermitian theory of atomic and molecular absorption, which enables computing the absorption spectrum of multi-electron atoms and molecules without using any fitting parameters. We propose a method for optically inducing exceptional points in atomic systems, and show that slight changes in the laser parameters may lead to dramatic changes in the absorption lineshape. We demonstrate these predictions for helium using exact ab-initio electronic-structure data. Finally, we derive a simple formula for the Fano asymmetry factor and evaluate it for a model xenon atom.

physics.chem-ph↗

arXiv2015

Atomic and molecular complex resonances from real eigenvalues using standard (hermitian) electronic structure calculations

Complex eigenvalues, resonances, play an important role in large variety of fields in physics and chemistry. For example, in cold molecular collision experiments and electron scattering experiments, autoionizing and pre-dissociative metastable resonances are generated. However, the computation of complex resonance eigenvalues is difficult, since it requires severe modifications of standard electronic structure codes and methods. Here we show how resonance eigenvalues, positions and widths, can be calculated using the standard, widely used, electronic-structure packages. Our method enables the calculations of the complex resonance eigenvalues by using analytical continuation procedures (such as Padé). The key point in our approach is the existence of narrow analytical passages from the real axis to the complex energy plane. In fact, the existence of these analytical passages relies on using finite basis sets. These passages become narrower as the basis set becomes more complete, whereas in the exact limit, these passages to the complex plane are closed. As illustrative numerical examples we calculated the autoionization resonances of helium, hydrogen anion and hydrogen molecule. We show that our results are in an excellent agreement with the results obtained by other theoretical methods and with available experimental results.

quant-ph↗