Research

On a broad perspective our research is focussed at the dynamics of strongly interacting quantum many-body systems. Much in the spirit of Feynman's concept of quantum simulation we develop ideas how to use well-controlled model systems, such as atoms at ultracold temperatures, to approach problems from condensed matter and high energy physics. For this we develop analytical and numerical tools to model and simulate these systems and search for efficient ways to prepare and probe interesting quantum states of matter. A list of current research interests can be found below. For those who want to dive in deeper, feel free to have a look at our recent publications.

Entanglement generation and detection

According to Erwin Schrödinger entanglement is the characteristic treat of quantum mechanics. It can be understood as some sort of correlation that seems to be incompatible with our intuitive classical understanding of correlations between spatially separated particles. Also, it has been realized that entanglement can be considered as a resource that enables applications such as quantum cryptography and quantum computing to outperform their classical counterparts. Motivated by both the fundamental and applied aspects we seek to develop new techniques to create and detect entanglement in clouds of ultracold atoms. A recent breakthrough was the detection of EPR steering in a spinor Bose-Einstein condensate. This experiment proves that non-local entanglement is naturally created in ultracold atomic clouds and can be made accessible by techniques as simple as expanding a condensate in a wave guide potential. For more details check out our recent preprint.

Unequal-time correlations - many-body spectroscopy

An interacting quantum many-body system can be characterized by analyzing its response to a weak perturbation. In the case of a spinor BEC this could be a small rotation of the collective spin. By observing the dynamics of the system following such a perturbation, i.e. the spatial and temporal correlations that develop, one can extract the dynamic structure factor, a key quantity in linear response theory. Knowledge of the dynamic structure factor provides a complete picture of the emerging quasi-particle modes in the many-body system, their excitation energy, lifetime and mean occupation number.

Our goal is to device protocols that allow to measure the dynamic structure factor in and out of equilibrium using novel techniques for manipulating BECs.

Many-body echo protocols

During the last few decades the field of atomic, molecular, and optical physics has seen overwhelming advances in preparing and controlling ensembles of atoms on the level of their quantum mechanical degrees of freedom. Recently, it has been shown that the engineering of the quantum mechanical evolution can be taken to the point of time-reversing the entire evolution of an interacting quantum system (Phys. Rev. Lett. 117, 013001 (2016), Nat. Phys. 13, 781–786 (2017)). This new capability opens the door to various applications, ranging from quantum enhance precision measurement to fundamental questions about the thermalization of closed quantum systems, and verification of quantum simulators. We seek to develop a better understanding of how time-reversal protocols can be used for accessing properties of quantum systems out of equilibrium such as their correlations and entanglement (arXiv:1706.01616).

Artificial neural network representations of quantum states

Artificial neural networks have proven extremely successful for machine learning tasks such as computer vision and speech recognition. Recently, reinforcement learning techniques have been applied for calculating the ground states and time evolution of quantum many-body problems (Science 355, 602 (2017)). Motivated by these findings we try to develop novel numerical techniques for solving the quantum many-body problem using machine learning techniques with a focus on artificial neural networks.

 
up