Temporal Localisation of Waves from Imaginary Line-Gap Topology
Abstract
For non-Hermitian Hamiltonians, gain, loss, and non-reciprocity produce complex eigenvalues which, in turn, facilitate different kinds of topological phases. One example is the imaginary line-gap phase, where eigenvalues cannot lie on the real line. This notion was recently shown to explain the robust temporal localisation of waves in photonic quantum walks and time-varying metamaterials. In these systems, waves localise around a time interface between topologically inequivalent mediums. At the core of this phenomenon is a π«π―-symmetric two-mode model, where the non-trivial topology arises due to the β€2 classification of the AI symmetry class. In this work, we study two-mode models in all non-Hermitian symmetry classes. We find that robust temporal localisation generically follows as a physical consequence of imaginary line-gap topology according to a simple diagnostic: at least one of time-reversal symmetry (π―hspace0.05em2 = 1) and particle-hole symmetry (π2 = 1) must be present. Our results provide a comprehensive symmetry-based guide to the observation of the topologically protected temporal localisation of waves.
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BibTeX
@misc{camacho2026temporal,
title = {{Temporal Localisation of Waves from Imaginary Line-Gap Topology}},
author = {Carlos Camacho and Tom Sheppard and Joshua Feis and Oliver Ashfield and Alexander Szameit and Frank Schindler and Hannah M. Price},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.11577},
eprint = {2609.11577},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.11577},
}
RIS
TY - UNPB
TI - Temporal Localisation of Waves from Imaginary Line-Gap Topology
AU - Carlos Camacho
AU - Tom Sheppard
AU - Joshua Feis
AU - Oliver Ashfield
AU - Alexander Szameit
AU - Frank Schindler
AU - Hannah M. Price
PY - 2026
DA - 2026/09/11
PB - arXiv
DO - 10.48550/arxiv.2609.11577
UR - https://arxiv.org/abs/2609.11577
AB - For non-Hermitian Hamiltonians, gain, loss, and non-reciprocity produce complex eigenvalues which, in turn, facilitate different kinds of topological phases. One example is the imaginary line-gap phase, where eigenvalues cannot lie on the real line. This notion was recently shown to explain the robust temporal localisation of waves in photonic quantum walks and time-varying metamaterials. In these systems, waves localise around a time interface between topologically inequivalent mediums. At the core of this phenomenon is a π«π―-symmetric two-mode model, where the non-trivial topology arises due to the β€_2 classification of the AI symmetry class. In this work, we study two-mode models in all non-Hermitian symmetry classes. We find that robust temporal localisation generically follows as a physical consequence of imaginary line-gap topology according to a simple diagnostic: at least one of time-reversal symmetry (π―^hspace0.05em2 = 1) and particle-hole symmetry (π^2 = 1) must be present. Our results provide a comprehensive symmetry-based guide to the observation of the topologically protected temporal localisation of waves.
ER -