# Welcome

The research in our group at the Department of Physics of the Technical University of Munich (TUM) focuses on condensed matter theory and 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 also been developed to study dynamic processes in condensed matter systems. We develop both analytical and numerical techniques to explore the far-from-equilibrium quantum dynamics of these systems and 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.

[1] | Floquet prethermalization and regimes of heating in a periodically driven, interacting quantum system. S. A. Weidinger, M. Knap, Sci. Rep. 7, 45382 (2017). |

[2] | Scrambling and thermalization in a diffusive quantum many-body system. A. Bohrdt, C. B. Mendl, M. Endres, M. Knap [arXiv:1612.02434]. |

[3] | 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). |

[4] | Far-from-equilibrium field theory of many-body quantum spin systems: Prethermalization and relaxation of spin spiral states in three dimensions. M. Babadi, E. Demler, M. Knap, Phys. Rev. X 5, 041005 (2015). |

## 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.

[1] | Noise-induced subdiffusion in strongly localized quantum systems. S. Gopalakrishnan, K. R. Islam, M. Knap [arXiv:1609.04818]. |

[2] | Periodically Driving a Many-Body Localized Quantum System. P. Bordia, H. Lüschen, U. Schneider, M. Knap, I. Bloch Nature Phys. AOP (2017). |

[3] | Anomalous diffusion and Griffiths effects near the many-body localization transition. K. Agarwal, S. Gopalakrishnan, M. Knap, M. Mueller, E. Demler, Phys. Rev. Lett. 114, 160401 (2015). |

## Transport and topology in condensed matter systems

Condensed matter systems with certain symmetries can have peculiar transport properties. We are interested in semimetals in which both electrons and holes contribute to transport, including HgTe quantum wells close to the topological insulator to metal transition. We also studied interaction effects in Weyl semimetals with either broken time-reversal or inversion symmetry. Weyl semimetals exhibit linearly-dispersing excitations at low energy which lead to unusual electrodynamic responses.

[1] | Transport in two-dimensional disordered semimetals. M. Knap, J.D. Sau, B.I. Halperin, E. Demler, Phys. Rev. Lett. 113, 186801 (2014). |

[2] | Interacting Weyl semimetals. W. Witczak-Krempa, M. Knap, D. Abanin, Phys. Rev. Lett. 113, 136402 (2014). |