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Non-Hermitian Quantum Systems: Emergent Phenomena and New Paradigms

A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Statistical Physics".

Deadline for manuscript submissions: 31 July 2026 | Viewed by 693

Special Issue Editors


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Guest Editor
Department of Physics, National University of Singapore, Singapore, Singapore
Interests: quantum many-body systems; quantum simulation; cold-atom systems; quantum computing
Special Issues, Collections and Topics in MDPI journals

E-Mail Website
Guest Editor
Department of Physics, National University of Singapore, Singapore, Singapore
Interests: quantum simulation; non-equilibrium physics; topology; quantum information
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Non-Hermitian quantum systems have emerged as a powerful and unifying framework for describing a broad class of physical phenomena that lie beyond the traditional paradigm of closed, unitary quantum mechanics. In such systems, non-Hermiticity naturally arises from dissipation, gain, measurements, nonreciprocal transport, and coupling to external environments. In recent years, research on these systems has revealed a wealth of emergent phenomena with no direct Hermitian counterparts, motivating the development of new theoretical frameworks and experimental strategies.

A defining characteristic of non-Hermitian quantum physics is the profound restructuring of spectral properties. The emergence of complex energy spectra, biorthogonal eigenstates, and eigenmode non-orthogonality fundamentally reshapes conventional notions. Moreover, non-Hermitian systems have also transformed contemporary views on topology. The discovery of non-Hermitian topological phases and the non-Hermitian skin effect has uncovered intrinsically non-Hermitian forms of boundary sensitivity, modified bulk–boundary correspondence, and novel topological invariants, highlighting the fundamentally emergent nature of topology in non-unitary settings. From the perspective of quantum information and statistical physics, non-Hermitian dynamics raise fundamental questions concerning entanglement structure and information flow. Effective non-Hermitian descriptions can be employed to model measurement-induced dynamics and post-selected evolution.

The rapid expansion of this field has been driven by a close interplay between theory and experiment. Emergent non-Hermitian phenomena have been realized across a wide range of platforms, including photonic and acoustic lattices, electronic materials, ultracold atoms, and programmable quantum simulators, underscoring the universality and versatility of non-Hermitian paradigms.

This Special Issue will provide a comprehensive snapshot of current advances in non-Hermitian quantum systems, with particular emphasis on emergent phenomena and new paradigms. We welcome original research articles, reviews, and perspectives addressing topics including, but not limited to, non-Hermitian spectral theory and topology; PT and generalized symmetries; exceptional points and criticality; entropy and information in non-unitary quantum dynamics; measurement-induced phenomena; and experimental realizations across quantum and classical platforms.

Dr. Ruizhe Shen
Prof. Ching Hua Lee
Guest Editors

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Keywords

  • non-Hermitian quantum systems
  • non-unitary dynamics
  • open quantum systems
  • parity–time (PT) symmetry
  • exceptional points
  • non-Hermitian topology
  • non-Hermitian skin effect
  • biorthogonal quantum mechanics
  • entanglement dynamics
  • measurement-induced phenomena
  • dissipative quantum systems
  • post-selected quantum dynamics
  • quantum simulators
  • non-Hermitian phase transitions
  • Lindblad dynamics

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Published Papers (1 paper)

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Research

18 pages, 12792 KB  
Article
Exact Solution and Large-Scale Scaling Analysis of the Imaginary Creutz–Stark Ladder
by Yunyao Qi, Heng Lin, Quanfeng Lu, Dan Long, Dong Ruan and Gui-Lu Long
Entropy 2026, 28(3), 259; https://doi.org/10.3390/e28030259 - 27 Feb 2026
Viewed by 454
Abstract
We present an analytical solution for the complex spectrum of a Creutz ladder subject to an imaginary Stark potential. By mapping the system to a momentum-space differential equation, we derive the closed-form solution for the momentum-space wavefunctions. We identify a distinct cross-shaped spectrum [...] Read more.
We present an analytical solution for the complex spectrum of a Creutz ladder subject to an imaginary Stark potential. By mapping the system to a momentum-space differential equation, we derive the closed-form solution for the momentum-space wavefunctions. We identify a distinct cross-shaped spectrum consisting of discrete localized sectors and a continuous branch of asymptotically real states. Our derivation reveals that the discrete sectors arise from a global phase winding condition, whereas the asymptotically real branch emerges when the energy magnitude is smaller than the inter-cell hopping strength, a regime in which the momentum-space wavefunction develops singularities. We demonstrate that these singularities prevent standard quantization; instead, the open boundary conditions are satisfied via a size-dependent imaginary energy component that regulates the wavefunction decay. To investigate the properties of this branch in the thermodynamic limit, we perform large-scale finite-size scaling analysis up to system sizes L109. The numerical results confirm the power-law decay of the residual imaginary energy, supporting the asymptotic reality of these states. Furthermore, scaling of the inverse participation ratio and fractal dimension indicates that these states, while exhibiting size-dependent localization in finite systems, evolve into an extended phase in the thermodynamic limit. Our results establish a theoretical framework for understanding spectral transitions in systems with imaginary Stark potentials, with potential realizations in photonic frequency synthetic dimensions. Full article
(This article belongs to the Special Issue Non-Hermitian Quantum Systems: Emergent Phenomena and New Paradigms)
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