The main focus of our research group is the theory of atomic, solid state and photonic systems, both with a conceptual interest towards their many-body dynamics, as well as for the purpose of developing functionalities for quantum technologies.
Ultra-fast dynamics in superconductors
We investigate light-induced dynamics in superconductors. One purpose is the understanding and optimization of light-controlled superconductors, featuring light-enhanced or light-induced superconductivity. Furthermore, novel, genuinely non-equilibrium states can be induced, such a time crystals of superconductors. Finally, we explore new technological applications of superconductors. We investigate these dynamical regimes both numerically and analytically. A key platform are high Tc superconductors.
Light-induced dynamics in 2D materials
As a second class of light-driven solids, we study 2D materials, such as graphene. We explore the light-induced electron dynamics in these solids, and the emergent signature in the transport properties, such as the Hall conductivity, as well as ARPES observables. Furthermore, we consider hybrid light-matter systems based on 2D materials.
Many-body dynamics in ultra-cold atom systems
The field of many-body dynamics is one of the fundamental frontiers of condensed matter theory. Ultra-cold atom experiments provide the ideal environment to study this field, because of the high level of tunability and control. We use both numerical methods, such as the Truncated Wigner approximation, and analytical approaches, such as renormalization group ideas, to understand this rich field.
Recent projects include the investigation of a dynamic Kosterlitz-Thouless transition in two dimensional Bose gases, the description of photoconductivity of fermionic atoms in an optical lattice via non-linear dynamics, and superfluid properties of ultra-cold atoms in a toroidal trap.
“Quantum engineering” of many-body phases with ultra-cold atoms
We study many-body phases in ultra-cold atom systems. In particular, the physics of ordered states in lower dimensions has a fascinating richness. We use Luttinger liquid theory, as an analytical tool, and time-evolving block decimation, as a numerical method, to study the quantum phases of one-dimensional systems. The method of functional renormalization group calculations is used to study competing orders of Fermi systems in two dimensions.
Recent projects include the investigation of Fermi gases in an optical lattice that interact via dipolar and quadrupolar interactions. Another recent project was the investigation of one-dimensional Bose-Fermi mixtures in the strong coupling regime.
Advancement of the technology of ultra-cold atom systems
The technological development of cooling and manipulating ultra-cold atoms has been one of the important achievements in physics over the last decades. One of our objectives is to contribute to the technological advancement of the field. We develop ideas for cooling techniques, and study measurement approaches, such as extracting the noise correlations from time-of-flight images.
Recent projects include the detection of counterflow and paired superfluid order via noise correlations and via dipole oscillations.
On the conceptual side of many-body theory, we advance the theory of path integrals, which we generalize towards squeezed-field path integrals. Here, the path integral is formulated via squeezed coherent states, rather than via coherent states, as it is done conventionally. This generalization of the Feynman path integral provides a new perspective on the relation of quantum and classical dynamics, and on collective modes in many-body systems. Furthermore, it provides a framework to develop new many-body methods, ranging from renormalization group methods to methods of correlated states of matter.
Quantum machine learning
We develop machine learning methods for the purpose for controlling quantum dynamics, and for the implementation of quantum computing algorithms. These studies are targeting both conceptual questions, as well as concrete experimental realizations, such as Rydberg atom based implementations, as well as superconducting qubits.