Control of entanglement in atomic ionization and decay processes
Dr. Stephan Fritzsche (Universität Kassel)

Today, entanglement in composite systems plays an important role in different fields of physics, from basic research up to the first successful devices in quantum engineering. Despite of recent advancements in understanding the basic principles of quantum information systems, however, there are still a large number of difficulties to be solved. One of the great challenges, for instance, refer to the decoherence in quantum systems and to the coupling of these systems with their environment.

To overcome these difficulties, several schemes for studying the decay of quantum states and for the creation of entanglement have been developed in the past decade, including a variety of measures, decoherence-free subspaces as well as (quantum) error correction codes.

In this contribution, density-matrix theory is applied in order to analyze how quantum entanglement can be manipulated and transfered in atomic photoionization and decay processes. Detailed calculations on the entanglement between the spins of the photoelectron and the remaining (photo-) ion have been carried out for both, hydrogen-like ions as well as for atomic strontium, as function of the energy and polarization of the incoming light, the nuclear charge of the ions as well as the emission angle of the photoelectrons. Similar investigations were performed also for the two-photon decay and enable us to characterize pairs of photons with a well-defined degree of entanglement.