Nonequilibrium quantum dynamics of correlated systems

Nonequilibrium quantum dynamics plays an important role in various fields rooted in both natural sciences as well as applied sciences. Among them are ultrafast laser spectroscopy and transport phenomena in condensed matter physics, quantum optics, semiconductor devices, and also cosmology. In several systems of these diverse fields the constituents are strongly correlated and manybody effects have to be taken into account to fully understand their physics. The enormous progress in controlling optical and atomic systems lead to the advent of "synthetic" manybody systems, including ensembles of ultracold atoms and light matter systems. One key property of synthetic manybody systems is that microscopic parameters are extremely well known and also highly controllable. This renders synthetic manybody systems as ideal candidates for studying nonequilibrium quantum dynamics and also poses new challenges for theory since vastly different energy and time scales are relevant as compared to condensed matter physics. Here, I propose to study on the one hand the transient manybody dynamics of correlated impurity systems, following a very special, local quantum quench, whose protocol is determined by established quantum optics tools of Ramsey, Hahn spin-echo or Rabi type. The proposed experiments, allow to explore universal impurity physics in regimes not accessible in more traditional condensed matter experiments. On the other hand, I am interested in the nonequilibrium steady state of light matter systems, where questions concerning phases and their quantum criticality seem to be extremely relevant. From finding answers to these questions, I also hope to contribute in answering the global theoretical question about universality in the nonequilibrium quantum dynamics of strongly correlated manybody systems. Insight into nonequilibrium properties of quantum manybody systems obtained from a fruitful interplay between experiments and theory of synthetic manybody systems might help to pave the way for the improvement and invention of high-tech applications, which might be rooted in the fields of material science, energy sciences, or quantum information sciences.

The aim of this Schrödinger fellowship was to study the dynamics of many particles on the microscopic scale of atoms where quantum mechanics is important. Quantum mechanics, the theory which explores the very smallest types of matter, has many surprising and baffling facets. For instance electrons can at the same time behave as a particle and as a wave. Even though it seems that quantum mechanics is very abstract there are several applications we use in our daily life which rely on this intriguing theory. Examples include transistors, which are the basic elements of computers or mobile phones, high precision clocks, used for the Global Positioning System (GPS), lasers with diverse applications in modern surgery or in DVD players, and Magnetic Resonance Imaging (MRI), which is used to reconstruct a three dimensional picture of our bodies without any exposure of radiation. In this project we studied the nonequilibrium dynamics of quantum systems which consist of many interacting particles. One crucial aspect is that many quantum particles can lead to phenomena which cannot be understood from a single particle level alone. In some sense these particles form teams to achieve goals which they could not achieve on the individual level. These phenomena are therefore called collective phenomena in the literature. A deep understanding of such phenomena could revolutionize our daily lives. However, until this point can be reached a lot of research has to be performed, particularly on the fundamental level, which was the aim of this project. We studied collective phenomena on very general grounds, tried to find interesting and potentially useful effects, and to gain understanding of how universal the observed phenomena are. In order to understand the quantum mechanics of these complex systems, we perform high accuracy computer simulations on big computer clusters and also apply complex analytical techniques. Furthermore, we collaborate with experimental colleagues who can realize the ideas we propose in their laboratories and experimentally proof our concepts. The research goals of this project have been to understand the fundamental properties of nonequilibrium quantum dynamics. Further progress in this field, which requires the collaboration of scientists all over the world, might revolutionize technology in our daily lives.