Research

Our group develops theoretical and computational methods to address open problems in strongly coupled quantum field theories. In particular, we design new algorithms using lattice field theory, tensor networks, deep learning, and quantum computing to study models ranging from (1+1) to (3+1) dimensions, with applications in particle and condensed matter physics. Our work is carried out in collaboration with theoretical and experimental physicists, mathematicians, and computer scientists.

We develop quantum algorithms for simulating lattice gauge theories on near-term and early fault-tolerant devices, exploiting the physical structure of the target Hamiltonians to improve algorithmic performance and resource efficiency. Our current research directions include:

Variational Quantum Algorithms 

Development of tailored ansatz circuits for computing ground states of 2+1D lattice gauge theories using the Variational Quantum Eigensolver (VQE), with a focus on adaptive construction strategies (ADAPT-VQE), symmetry-informed operator pools, and convergence analysis.

Sampling-based Krylov Quantum Diagonalization 

Study of quantum algorithms based on real-time evolution for sampling Krylov subspaces, enabling efficient ground-state approximation within reduced Hilbert spaces.

Qudit Architectures

Exploratory research on qudit-based quantum computing architectures for lattice gauge theory simulations, which offer a promising route toward more resource-efficient and accurate simulations of higher-dimensional systems.

We develop and apply tensor network methods to study lattice field theories and strongly coupled quantum many-body systems, targeting physical regimes beyond the reach of conventional Monte Carlo approaches. Our current research directions include:

Tree Tensor Networks 

Application of exact diagonalization and tree tensor network methods to lattice gauge theories in (3+1) dimensions, with the aim of simulating topological terms and exploring the resulting phase structure.

Matrix Product States

Computation of the step-scaling function in the Hamiltonian formulation of 2+1D U(1) gauge theory using matrix product states.

Entanglement Measures

Investigation of entanglement measures in strongly interacting quantum many-body systems and quantum field theories, using a combination of Monte Carlo simulations and tensor network techniques.

We develop and apply machine-learning methods to improve sampling and optimization in lattice field theories and strongly coupled quantum many-body systems. Our current research directions include:

(Stochastic) Normalizing Flows and Non-equilibrium Monte Carlo 

Development of machine-learning-based methods for ergodic simulation of strongly coupled lattice systems, including the Hubbard model and (non)Abelian gauge theories, using normalizing flows, stochastic normalizing flows, non-equilibrium Monte Carlo simulations, and annealing-based techniques.

Density of States with Normalizing Flows

Investigation of the density of states method for lattice field theories with a sign problem, applied to the Hubbard model and U(1) gauge theory, using normalizing flows to reconstruct the generalized density of states.

Optimization Methods

Development of an Extreme Value Extension (EVE) to the Adaptive Moment Estimation (ADAM) optimizer, designed to improve robustness in highly ill-conditioned optimization problems arising in lattice field theory applications and beyond.

We study Quantum Chromodynamics on the lattice, with a focus on finite-density regimes and the development of improved computational methods. Our current research directions include:

Lattice QCD at Finite Density

Study of lattice QCD at finite chemical potential, addressing the sign problem via imaginary chemical potential and Lefschetz thimbles, with application to the QCD phase diagram.

Method Development for Lattice QCD

Development of methods for reconstructing spectral functions and transport coefficients from Euclidean correlators, as well as for flexible interpolation of lattice QCD observables across bare parameters using conditional masked autoregressive flows.

Theses

Opportunities to join the group are available at Bachelor and Master level. If you are interested, please send your research interests and transcripts to hiskp-funcke-group@listen.uni-bonn.de. A list of previous Bachelor and Master thesis topics can be found below.

2026: Nico Dichter, "Advancing variational quantum algorithms for (2+1)-dimensional fermionic systems"
2025: Emil Rosanowski, "Variational Quantum Eigensolver for (2+1)D Quantum Electrodynamics at Finite Density"
2025: Janik Kreit, "Symmetry-informed Normalizing Flows for Lattice Field Theories"
2024: Luca Johannes Wagner, "Using Machine Learning for Noise Resilient Optimization of Variational Quantum Eigensolvers"

2025: Elisabeth Grete von Wolff, "Machine-Learning-Enhanced Quantum Algorithms for Simulating 2+1D Quantum Electrodynamics"
2024: Jannik Niebling, "Machine Learning for Integrating Highly Oscillatory Functions"
2023: Felicitas Freche, "Quantum gravity prediction for the equation of state parameter of dark energy"

Coordinated Research Programs

Our research is funded by and embedded in three coordinated research programs, with further details on each provided below.

The CRC1639 NuMeriQS is an interdisciplinary collaborative research center funded by the DFG, bringing together scientists from theoretical chemistry and theoretical physics with numerical mathematicians and computer scientists.


Link to the webpage
: https://numeriqs.hiskp.uni-bonn.de/

The Cluster of Excellence “Color meets Flavor” (CmF) addresses fundamental questions about the nature of matter and the fundamental forces by combining the expertise of world-renowned experts in strong and weak interaction physics and the leading experiments in the field. Among the most exciting results in particle physics of recent years are the observation of exotic bound states of quarks as well as intriguing measurements of the decays of heavy quarks. Since quarks are not observed as free particles but form bound states, their study requires a precise understanding of both the strong force responsible for their binding and the weak force involved in their decays. This interplay between color and flavor is tackled by research groups from Bonn, Dortmund, Siegen, and Jülich.

Link to the webpage: https://color-meets-flavor.de/

The Cluster of Excellence “Matter and Light for Quantum Computing (ML4Q) is a consortium of scientists with backgrounds in the key disciplines of quantum computation: condensed matter physics, quantum optics, quantum devices, and quantum information. We aim to push the frontiers of the field by developing novel forms of quantum hard- and software: from fundamental research on quantum matter over quantum information devices to operation protocols and software. Our research focus is on pioneering technologies that are at an early development stage today, but may become game changers tomorrow. ML4Q is the project synergizing the Rhineland into a hub in quantum computing research. A key part of our mission is the training of the next generation of researchers that will pull quantum computation past the application threshold.

Link to the webpage
: https://ml4q.de/

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