Computational atomic physics

Electron-ion recombination

The electron-ion recombination processes are essential for a fundamental understanding of interactions in atoms and ions and have also astrophysical relevance. Experimental studies in storage rings where cold ions and electrons collide with a well defined relative energy allow us to follow the recombination process in detail. The studies are performed for ions of almost any degree of ionization. We work in close connection with experiments, performed for example at the S-EBIT (Stockholm Electron Beam Ion Trap) or at storage rings like CRYRING in Stockholm, TSR in Heidelberg, and also at GSI in Darmstadt. Since it is necessary to describe doubly excited states in medium or highly charged ions where a relativistic treatment is essential we have developed a scheme based on relativistic many-body perturbation theory combined with the method of complex rotation. 

A few recent related publications:  PRL 100,  JPB 40,  A and A 459,  PRL 95


Time-dependent problems in atomic systems, interaction of atoms with laser pulses

With the constant intensity increase and duration decrease of experimentally available laser pulses, more and more advanced theoretical models are necessary to describe their interaction with atoms. In particular, it is sometimes necessary to go beyond the dipole approximation and work with the Dirac equation rather then with the Schrödinger equation. We apply different methods, like complex scaling or Magnus propagator for explicitly time-dependent Hamiltonians and Floquet theory, to analyze ionization spectra, ionization probabilities and population of states in atoms exposed to electromagnetic fields. 

A few recent related publications:  PRA 79,  PRA 78,  PRL 105,  PRA 85


Quantum dots, dot molecules and rings

Since the beginning of the 1990's a new field has developed on the border between solid state, condensed matter and atomic physics. The possibility to confine a small and controllable number of electrons in tunable electrostatic potentials inside semiconductor materials has been vastly explored in this new field nowadays known as quantum dots and quantum rings physics. The interest for quantum dots and rings is mainly motivated by the fact that they can be used as building blocks for the construction of nanoelectronic devices, in the future possibly even as q-bits i.e. the essential part of quantum computers. We perform structural many-body perturbation theory calculations on quantum dots and also work with possible applications in quantum information processing. 

A few recent related publications:  PRB 81 (1),  PRB 81 (2),  PRB 79 (1),  PRB 79 (2),  PRB 76 (1),  PRB 76 (2)


Decoherence and open quantum systems

Open quantum systems have become more and more important during the last decades, covering a wide spectrum of applications in surface, atomic, nuclear and particle physics. In particular, they present a crucial framework in quantum information theory which makes it possible to study fundamental aspects like dephasing and entanglement dynamics and environmentally induced loss of quantum coherence ususally called decoherence. The resulting non-unitary time evolution is often described by so called master equations for the density matrix. We use one of the most common, the Lindblad master equation, to study open atomic systems and devices that are potential candidates for a quantum computer basis, like quantum dots or ion traps. 

A few recent related publications:  PRA 80,  JPA 42 (1),  PRB 79 (1),  JPA 42 (2),  JPA 41


Multiply excited states in atoms and ions

Doubly excited states are very sensitive to correlation and the usual independent particle models can often not even give a qualitative description of them. These states thus provide good test cases for studies of correlation. For such studies few-body systems with two or three electrons are especially interesting since they are within reach for a complete ab initio treatment. Doubly excited states, which in general are autoionizing, are also important as intermediate states in many physical processes. Their description is essential to describe ionization of many-electron systems by photons or other particles, to understand the decay of states with inner shell vacancies or to describe electron-ion recombination for non-bare ions. 

A few recent related publications:  EPJD 51,  JPB 40,  JPB 37


Negative ions and photodetachment

In negative ions the last electron is, in general, bound only due to the dipole part of the electron-electron interaction, which is attractive. Many negative ions have just one bound state but often also long-lived resonant states exist which can be observed in photodetachment studies. We have worked with H-, Li- and He- which has been treated from first principles as a full three-body system. 

A few recent related publications:  PRA 78,  PRA 68


Highly charged ions and inner shell vacancies in heavy elements

Inner shell vacancies in heavy elements are in general unstable and decay by electron or photon emission. Accurate X-ray spectroscopy of the emitted photon when the system make a transition between the the K, L and M shells gives information about relativistic and radiative effects. During a long time collaboration with the group of Paul Indelicato in Paris we have combined different numerical approaches and calculated a large number of transition energies for elements with nuclear charges ranging from Z=10 -100. 

A few recent related publications:  PRA 73,  Rev. Mod. Phys. 75