# SKM 2023 – wissenschaftliches Programm

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# DY: Fachverband Dynamik und Statistische Physik

## DY 21: Quantum Chaos and Coherent Dynamics

### DY 21.4: Vortrag

### Dienstag, 28. März 2023, 14:45–15:00, MOL 213

**A spectral duality in graphs and microwave networks** — •Tobias Hofmann^{1}, Junjie Lu^{2}, Ulrich Kuhl^{1, 2}, and Hans-Jürgen Stöckmann^{1} — ^{1}Fachbereich Physik, Philipps-Universität Marburg, 35032 Marburg, Germany — ^{2}Institut de Physique de Nice, CNRS, Université Côte d'Azur, 06108 Nice, France

Quantum graphs and their experimental counterparts, microwave networks, are ideally suited to study the spectral statistics of chaotic systems. The graph spectrum is obtained from the zeros of a secular determinant derived from energy and charge conservation. Depending on the boundary conditions at the vertices, there are Neumann and Dirichlet graphs. The first ones are realized in experiments, since the standard junctions connecting the bonds obey Neumann boundary conditions due to current conservation. On average, the corresponding Neumann and Dirichlet eigenvalues alternate as a function of the wave number, with the consequence that the Neumann spectrum is described by random matrix theory only locally, but adopts features of the interlacing Dirichlet spectrum for long-range correlations. Another spectral interlacing is found for the Green's function, which in contrast to the secular determinant is experimentally accessible. This is illustrated by microwave studies and numerics.