Current Research Directions

Project Leader: Titus Neupert
Main Contributors: Andrea Kouta Dagnino, Gerrit Niederhoff, Hao Chen, Simon Hans Hille, Attila Szabó, Juraj Hasik

Compared to classical systems, quantum many-body systems are notoriously hard to simulate on classical computers. With a focus on quantum magnets and systems of interacting electrons, we explore regimes in which correlations between the degrees of freedom are strongest and perturbative approaches fail. Specifically, we explore innovative variational schemes that either involve wave functions constructed from neural networks or tensor networks (iPEPS).

"Variational benchmarks for quantum many-body problems", Science 386, 296 (2024)

"Algorithmic Error Mitigation Scheme for Current Quantum Processors", Quantum 5, 492 (2021)

Project Leaders: Titus Neupert, Mark H. Fischer
Main Contributors: Bernhard E Lüscher, Sofie Castro Holbæk

Crystals realizing a kagome lattice exhibit a host of phenomena related to their lattice geometry, topological electron behaviour and the competition between different possible ground states. A particularly interesting family are the compounds of AVS (KV3Sb5, CsV3Sb5 and RbV3Sb5), with a kagome net of vanadium atoms. These materials feature an unconventional cdw below approx 100K and superconductivity at low temperature. In our group, we study these phases both on theoretical grounds, as well as in close collaboration with experimental colleagues.

Key Publications:

• "Switchable chiral transport in charge-ordered kagome metal CsV₃Sb₅", Nature 611, 461 (2022)
• "Correlated order at at the tipping point in the kagome metal CsV₃Sb₅", Nature Physics 20, 579 (2024)
• "Chiral kagome superconductivity modulations with residual Fermi arcs", Nature 632, 775 (2024)
• "Unconventional Gapping Behavior in a Kagome Superconductor", Nature Physics 21, 556 (2025)

Project Leader: Titus Neupert
Main Contributors: Andrea Kouta Dagnino, Gerrit Niederhoff, Hao Chen, Nav Batra Juraj Hasik, Dan Mao, Valentin Leeb

We showed theoretically that the fractional qunatum Hall effect can appear without an external magnetic field, giving rise to so-called fractional Chern insulators. These states of matter have been found in van-der-Waals materials. We explore with analytical and numerical calculations, how to stabilize fractional Chern insulators, how non-Abelian phases can be realized and what novel probes could be used to detect them.

"Fractional Quantum Hall States at Zero Magnetic Field", PRL 106, 236804 (2011)

Project Leaders: Mark H. Fischer, Titus Neupert
Main Contributors: Sofie Castro HolbækBernhard E Lüscher

Superconductivity takes a particular role among correlated phases of quantum matter in that quantum physics is dramatically manifested in a macroscopic ‘classical’ observable, the (vanishing) resistivity. The Department of Physics at the University of Zurich has a strong tradition in the study of superconductors: the Nobel laureate Prof. Karl Alex Müller, who discovered high-temperature superconductivity in the Cuprates, was an emeritus and Prof. Andreas Schilling holds the world record for the highest transition temperature under ambient pressure. In our theoretical research, we are primarily interested in the interplay of superconducting order with topological features of materials, crystalline symmetries and strong spin-orbit coupling.

Key Publications: 

• "Superconductivity and Local Inversion-Symmetry Breaking", Annual Review of Condensed Matter Physics 14, 153 (2023)
• "Atomic limit and inversion-symmetry indicators for topological superconductors", Phys. Rev. Research 2, 013064 (2020)