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                                     “Non-Hermitian Topological Physics”




Thursday, 24 Nov. 2022

    Video-Recording for any system with MP4-support

   - Video.mp4  (ca. 453 Mb)

 15:15 – 16:30



                                                       Emil Bergholtz



Hermiticity is a fundamental aspect of isolated quantum systems. Nevertheless,

non-Hermitian effects are ubiquitous in both classical and quantum systems.

In the classical realm this is manifested e.g. as friction in mechanical systems,

resistivity in electrical circuits, and losses in optics. In the quantum realm

it reflects the dynamics of open systems, as well as decay, scattering, resonances

and broadening due to e.g. interactions and disorder. During the past few decades

notions of topology have revolutionised the understanding of matter as recognized

by several Nobel prizes. This understanding is however based on the topology

and stability of Hermitian matrices. In contrast, in the past few years, intense

theoretical and experimental research has revealed that non-Hermitian effects

dramatically enrich the phenomenology of topological physics—providing a

cross-disciplinary frontier that is rapidly expanding [1]. Using simple examples,

I will describe the essence of these developments starting with the non-Hermitian

concept of exceptional degeneracies at which both eigenvalues and eigenvectors

coalesce. I will also discuss how the bulk-boundary correspondence is radically

modified in non-Hermitian systems and how this might be harnessed in novel

sensor devices [2].


[1] E.J. Bergholtz, J.C. Budich, and F.K. Kunst, Reviews of Modern Physics 93, 15005 (2021).

[2] J.C. Budich and E.J. Bergholtz, Physical Review Letters 125, 180403 (2020).


Emil Bergholtz is the recipient of Göran Gustafsson Prize (KVA)


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