# Welcome

A young and dynamic group focusing on theoretical quantum many-body physics has been launched in July 2015 at the Department of Physics, Technische Universität München (TUM). The group is headed by Michael Knap and will study collective quantum dynamics.
Our research clusters around a broad range of questions from condensed matter theory and also bridges to quantum optics, atomic physics, quantum information, and computational sciences. Particular directions include:

## 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, dynamic phase transitions, intertwined order far from equilibrium, and the competition between coherence and dissipation.

[1] | 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). |

[2] | Probing real-space and time resolved correlation functions with many-body Ramsey interferometry. M. Knap, A. Kantian, T. Giamarchi, I. Bloch, M.D. Lukin, E. Demler, Phys. Rev. Lett. 111, 147205 (2013). |

[3] | Time dependent impurity in ultracold fermions: orthogonality catastrophe and beyond. M. Knap, A. Shashi, Y. Nishida, A. Imambekov, D.A. Abanin, E. Demler, Phys. Rev. X 2, 041020 (2012). |

## 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] | Low-frequency conductivity in many-body localized systems. S. Gopalakrishnan, M. Mueller, V. Khemani, M. Knap, E. Demler, D.A. Huse, Phys. Rev. B 92, 104202 (2015). |

[2] | 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). |

[3] | Interferometric probes of many-body localization. M. Serbyn, M. Knap, S. Gopalakrishnan, Z. Papić, N.Y. Yao, C.R. Laumann, D.A. Abanin, M.D. Lukin, E. Demler, Phys. Rev. Lett. 113, 147204 (2014). |

## 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). |