The research in our group clusters around a variety of questions on non-equilibrium quantum dynamics in ultracold quantum gases, correlated quantum materials, and interacting light-matter systems. Interactions and correlations in such systems often manifest in striking and novel properties which emerge from the collective behavior of the quantum particles. Our group develops both analytical and numerical techniques to elucidate the effects of strong interactions. An important factor of our research is also its immediate relevance for experiments, which leads to a close collaboration with various experimental groups.
Correlated quantum systems out of equilibrium
Recent conceptional and technical progress makes it possible to prepare and explore strongly-correlated non-equilibrium quantum states of matter. The tremendous level of control and favorable time scales achieved in experiments with synthetic quantum matter, such as ultracold atoms, polar molecules, or trapped ions, renders these systems as ideal candidates to explore non-equilibrium quantum dynamics. Furthermore, very powerful experimental techniques have been developed to study dynamic processes in condensed matter systems as well. These techniques are based on pump-probe spectroscopy on time scales reaching down to sub-femtoseconds. Such technology therefore makes it possible to manipulate and control material properties. We develop both analytical and numerical techniques to explore the far-from-equilibrium quantum dynamics of these systems. The techniques range from non-equilibrium field theories to exact numerical calculations based on matrix product states. We study fundamental questions including thermalization in closed quantum systems, emergent phenomena in periodically driven Floquet systems, dynamic phase transitions, intertwined order far-from-equilibrium, and the competition between coherence and dissipation.
- Scrambling and thermalization in a diffusive quantum many-body system. A. Bohrdt, C. B. Mendl, M. Endres, M. Knap, New J. Phys. 19, 063001 (2017).
- Floquet prethermalization and regimes of heating in a periodically driven, interacting quantum system. Simon A. Weidinger, Michael Knap, Sci. Rep. 7, 45382 (2017)
- Ultrafast many-body interferometry of impurities coupled to a Fermi sea. M. Cetina, M. Jag, R. S. Lous, I. Fritsche, J. T. M. Walraven, R. Grimm, J. Levinsen, M. M. Parish, R. Schmidt, M. Knap, E. Demler, Science 354, 96 (2016)
Disordered many-body systems
Disorder has a drastic influence on transport properties. In the presence of a random potential a system of interacting electrons can become insulating; a phenomenon known as many-body localization. However, even beyond the vanishing transport such systems have very intriguing properties. For example, many-body localization describes an exotic phase of matter, which is robust to small changes in the microscopic Hamiltonian. Moreover, fundamental concepts of statistical mechanics break down in the many-body localized phase. We study how these particular properties can be characterized by interferometric techniques, explore distinct experimental signatures of disordered systems, and analyze the transition from the localized to the delocalized phase.
- Periodically Driving a Many-Body Localized Quantum System. Pranjal Bordia, Henrik Lüschen, Ulrich Schneider, Michael Knap, Immanuel Bloch, Nature Phys. 13, 460 (2017).
- Noise-induced subdiffusion in strongly localized quantum systems. Sarang Gopalakrishnan, K. Ranjibul Islam, Michael Knap, Phys. Rev. Lett. 119, 046601 (2017).
- Anomalous diffusion and Griffiths effects near the many-body localization transition. Kartiek Agarwal, Sarang Gopalakrishnan, Michael Knap, Markus Mueller, Eugene Demler, Phys. Rev. Lett. 114, 160401 (2015)