# ProjectLocal Stable Gaps and Response in Interacting Many-Body Quantum Systems

## Basic data

Title:

Local Stable Gaps and Response in Interacting Many-Body Quantum Systems

Duration:

01/01/2023 to 31/12/2026

Abstract / short description:

The theoretical understanding of the quantum Hall effect has driven important developments in mathe- matics and mathematical physics over the past three decades and continues to do so. The most important aspects are the quantization of Hall conductivity, the validity of the linear response formalism, the role of random impurities, and the correspondence between bulk and boundaries. Only recently have important advances concerning quantization and linear response been made specifically for models of interacting fermions at zero temperature either on torus geometries or in the thermodynamic limit.

For systems without boundaries the starting point for the mathematical analysis of quantum Hall systems is a many-body Hamiltonian with a gapped ground state. In particular, such systems display exponential decay of correlations [HK06]. While establishing a spectral gap for a given many-body Hamiltonian is an important and difficult problem in itself (see for example Projects A7 and A8), for us the central question will be the local stability and the local response of gapped ground states resp. thermal states: starting from an extended fermionic gapped system describing the electrons in a Hall insulator on a torus geometry, the introduction of edges can be viewed as a local perturbation of the Hamiltonian near the new edges. Because of the appearance of edge states, such a perturbation closes the spectral gap above the ground state energy and introduces long-range correlations along the boundary.

In our project, we aim to further develop the mathematical tools necessary to understand adiabatic and linear response for systems with boundaries. To this end, we explore mathematical questions whose relevance is not limited to quantum Hall systems, but extends, for example, to quantum information. Conversely, we also intend to use new approaches recently developed in quantum information to solve these problems motivated from mathematical physics.

For systems without boundaries the starting point for the mathematical analysis of quantum Hall systems is a many-body Hamiltonian with a gapped ground state. In particular, such systems display exponential decay of correlations [HK06]. While establishing a spectral gap for a given many-body Hamiltonian is an important and difficult problem in itself (see for example Projects A7 and A8), for us the central question will be the local stability and the local response of gapped ground states resp. thermal states: starting from an extended fermionic gapped system describing the electrons in a Hall insulator on a torus geometry, the introduction of edges can be viewed as a local perturbation of the Hamiltonian near the new edges. Because of the appearance of edge states, such a perturbation closes the spectral gap above the ground state energy and introduces long-range correlations along the boundary.

In our project, we aim to further develop the mathematical tools necessary to understand adiabatic and linear response for systems with boundaries. To this end, we explore mathematical questions whose relevance is not limited to quantum Hall systems, but extends, for example, to quantum information. Conversely, we also intend to use new approaches recently developed in quantum information to solve these problems motivated from mathematical physics.

Keywords:

Mathematical Physics

Mathematical Quantum Theory

Spectral gaps

Adiabatic theory

## Involved staff

### Managers

Faculty of Science

University of Tübingen

University of Tübingen

Department of Mathematics

Faculty of Science

Faculty of Science

Department of Mathematics

Faculty of Science

Faculty of Science

### Other staff

Department of Mathematics

Faculty of Science

Faculty of Science

Department of Mathematics

Faculty of Science

Faculty of Science

## Local organizational units

Department of Mathematics

Faculty of Science

University of Tübingen

University of Tübingen

## Funders

Bonn, Nordrhein-Westfalen, Germany