Physikalische Kolloquien im Sommersemester 2022

Prof. Dr. Tommaso Calarco

Building the second quantum revolution: quantum control for quantum technologies

Quantum mechanics is at the basis of all present-day information and communication technologies: to name just two examples, transistors and lasers would be impossible to build without understanding the quantum behaviour of matter and light. But the control of individual quantum systems has long been considered only a “thought experiment”, something only possible in theory. However, today this is routinely achieved in labs around the world, and it is the basis of quantum technologies.

To achieve this vision in real environments, we need to push our ability to control the dynamics of increasingly complex quantum systems to its limits. In the case of quantum systems with few particles, the decoherence occurring due to the interaction with the environment hinders the realisation of desired processes. In quantum many-body systems, the complexity of their dynamics makes the state preparation by external manipulation more difficult. I will show that Quantum Optimal Control Theory provides an effective strategy to overcome these problems. Quantum coherence is used to achieve a desired target with high accuracy, even under real conditions. I present current experiments that have been made possible by our new optimal control algorithm, and explain how we can use such methods to push the limits of the physical realisation of quantum technologies.

Dr. Christin David
Institut für Festkörpertheorie  und -optik

Habilitationsvorstellung

Hybrid Nanostructures Systems beyond classical Electrodynamics: Mesoscale Dynamics and Nonlinear Effects

A key task in modeling nanoscale systems on the verge of the quantum regime is the integration of the quantum nature of atoms, electrons and molecules and their interaction with electromagnetic fields, the interplay of optically excited nanocrystals with complex energy transfer mechanisms stemming from electron transport. Mesoscale electron dynamics and rough surface morphologies are not typically captured in standard electrodynamics. Though such effects are highly localized, optical coupling can lead to an impact on a larger device via retardation and lattice effects. We investigate theoretically the optial properties of hybrid metal, dielectric and ionic largely regular nanostructures in the presence of nanosized features such as gaps and thin walls in tubular structures. We focus hereby on two aspects: (i) nonclassical effects stemming from the quantum nature of freely moving charges and (ii) nonlinear optical response. The overall aim is to realistically describe complex nanoparticle distributions and ultrathin multilayers with reliable and rapid methods of computational nanophotonics while extending its scope towards multiphysics aspects beyond classical electrodynamics with applications in sensing, spectroscopy and light harvesting devices.

Dr.  Sabine Körbel
Institut für Festkörpertheorie  und -optik

Habilitationsvorstellung

Polarons at ferroelectric domain walls in BiFeO3

Ferroelectric domain walls are atomically narrow planes that can behave very differently from the surrounding bulk ferroelectric material. For example, the domain walls in many ferroelectrics can collect and conduct charge carriers despite the insulating nature of the host material. Domain walls can be created, moved, and removed again in a controlled way, thus they can be used to tailor the electronic properties of the ferroelectric. Charge carriers that accumulate at domain walls may lead to metallic or semiconducting charge transport characteristics depending on whether they are delocalized or form self-trapped small polarons. The latter may be detected, for example, as deep levels within the band gap in optical absorption or photoluminescence spectra. First-principles materials modeling can help to interpret experimental findings and make predictions where experimental data are not available. In my talk I will present insights into polaron formation at ferroelectric domain walls in BiFeO3 gained from first-principles modeling.

Prof. Dr. Dario Polli

Prof. Dr. Reinhard Genzel
Nobelpreisträger für Physik

Max-Planck-Institut für extraterrestrische Physik, Garching

Öffentlicher Abendvortrag im Rahmen der bundesweiten Lehrerfortbildung "Astronomie"

A 40-year Journey / Eine vierzigjährige Reise