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arXiv · 2606.03789

Triple exceptional point with unitary paths of unfolding in a three-site fermionic Swanson-like model

Bijan Bagchi·Aritra Ghosh·Miloslav Znojil
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Abstract

A fermionic three-site generalization of the popular bosonic Swanson model is studied as providing an exactly solvable five-parametric example of the quantum-mechanical unitary-evolution process leading to an ultimate loss of the observability and fall in an exceptional-point singularity (EP3). The instant of degeneracy is found to have an explicit one-parametric form. Its unitarity-compatible vicinity (i.e., the corridor of access to EP3) is also specified in closed form. The exact, numerical-error-independent solvability is found essential due to another, avoided, false energy-level crossing which is found to occur not too far from the true EP3 singularity.

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Bijan Bagchi, Aritra Ghosh, Miloslav Znojil. 2026-06-02. Triple exceptional point with unitary paths of unfolding in a three-site fermionic Swanson-like model. https://doi.org/10.1016/j.aop.2026.170569

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