In the realm of contemporary physics, non-Hermitian systems have emerged as a fascinating frontier, revealing phenomena that challenge traditional quantum mechanics and open avenues for revolutionary technological applications. A recent breakthrough study titled “Coupled non-Hermitian skin effect with exceptional points,” published in Light: Science & Applications, presents a novel exploration of how coupling in non-Hermitian lattices can lead to extraordinary physical effects. This research illuminates the interplay between two intriguing phenomena—the non-Hermitian skin effect (NHSE) and exceptional points (EPs)—ushering in fresh insights into wave dynamics in open systems.
Non-Hermitian physics fundamentally departs from conventional Hermitian models by allowing energy exchange with the environment, often represented through complex potentials or gain and loss terms. This leads to non-unitary evolution and the emergence of counterintuitive effects, such as enhanced sensitivity and directional transport of waves. Among such phenomena, the non-Hermitian skin effect stands out due to its hallmark: an extensive accumulation of eigenmodes at the system boundaries, defying the well-known bulk-boundary correspondence principle that governs Hermitian systems. Understanding and harnessing NHSE is critical for next-generation photonic devices, sensors, and quantum simulators.
The study by Wang et al. ventures into the unexplored territory where multiple NHSE systems are coupled together, unveiling a landscape where exceptional points—a form of spectral degeneracy unique to non-Hermitian systems—interact with boundary mode localization to generate rich physical behaviors. Exceptional points are singularities in the parameter space of a non-Hermitian system where both eigenvalues and eigenvectors coalesce. These points are known for displaying peculiar topological structures and enhanced response to perturbations, which could be exploited in ultrasensitive detection schemes.
By constructing theoretical models and performing meticulous calculations, the researchers demonstrate that coupling two non-Hermitian lattices with distinct skin effects produces coupled modes whose spatial distributions and spectral properties are governed by a delicate balance between the NHSE and EPs. This coupling leads to phenomena never before observed: the skin modes do not simply add together, but instead hybridize and drastically reconfigure, causing abrupt shifts in localization and energy landscapes. These coupled systems exhibit what might be conceptualized as a “hybrid skin effect,” where the envelope of eigenstates and their spectral degeneracies become intricately intertwined.
One of the key technical insights in this work is the characterization of how the coupling modifies the Hamiltonian’s non-Hermiticity. The authors introduce a coupling matrix embedding asymmetric hopping amplitudes, which is pivotal to inducing the skin effect in each subsystem as well as enabling the formation of exceptional points in the combined system. This approach enables the pinpointing of parameter regimes where the NHSE and EP phenomena coalesce, thereby facilitating controlled transitions between different topological phases and spectral singularities. The controllability of these transitions is vital for real-world applications that rely on dynamically tunable system responses.
Delving deeper, the study applies the generalized Brillouin zone (GBZ) theory, an advanced mathematical framework developed to properly interpret bulk spectra in non-Hermitian lattices. The GBZ formalism allows the researchers to rigorously analyze the energy bands and eigenmode distributions under open boundary conditions, which contrasts starkly to the conventional Bloch band theory valid only under periodic conditions. Within this enhanced framework, Wang et al. trace how the coupled system’s GBZ manifests new complex contours in momentum space, reflecting the hybridization of skin modes and the resulting spectral singularities at exceptional points.
Such theoretical advancements could revolutionize how experimental physicists and engineers design photonic structures, electronic metamaterials, and acoustic devices. For instance, in photonics, manipulating skin modes and exceptional points can lead to unprecedented control over light propagation, enabling unidirectional lasers, robust signal routing, and novel sensing architectures that capitalize on enhanced modal overlaps and sensitivity near EPs. The coupling-induced skin effect hybridization reveals pathways to engineer device responses that are both resilient to fabrication imperfections and highly responsive to external stimuli.
Another notable implication of this work lies in its potential to deepen our understanding of topological phases in non-Hermitian systems. Topology in Hermitian physics has already found profound applications in robust electronic and photonic systems, but extending these concepts to non-Hermitian regimes has posed challenges due to the failure of many traditional invariants and symmetries. By systematically studying the coupling of NHSE-preserving lattices, the authors shed light on how topological invariants must be modified or generalized to accommodate the interplay between localization and spectral degeneracies, thereby expanding the theoretical toolkit available to researchers.
The researchers also investigate the dynamical consequences of their theoretical findings by simulating wave packet evolution in coupled non-Hermitian lattices. Their results indicate that the hybrid skin effect leads to asymmetric and highly nonreciprocal transport of wave packets, with amplification or attenuation dependent on initial conditions and the coupling parameters. This directional control of wave dynamics could find applications in information processing and communication technologies, where robust routing and amplification of signals in integrated platforms are critical.
Importantly, the experimental feasibility of realizing such coupled non-Hermitian systems is discussed. The study highlights realistic platforms including coupled optical waveguides, electric circuits, and mechanical metamaterials where gain and loss can be engineered with precision. Advances in nanofabrication and active material synthesis make the physical implementation of these concepts increasingly attainable. Such experiments would validate the predicted coupling-induced phenomena and potentially inspire further innovations in device design based on these principles.
Critically, the paper underscores the interplay between theory and experiment in non-Hermitian physics. While earlier studies focused predominantly on isolated systems, the coupling scenarios investigated here bring the field closer to the complexity encountered in realistic environments, where multiple non-Hermitian subsystems interact. This realism enhances the scientific relevance and technological impact of the results, marking a significant step towards integrating non-Hermitian physics into practical applications and devices.
Moreover, the coupling of non-Hermitian skin effects with exceptional points opens new avenues for fundamental physics research. The spectral topologies arising in coupled systems could lead to discoveries of novel phases of matter and unconventional quantum dynamics not attainable in Hermitian systems. By mapping these exotic phases, scientists could develop new paradigms for quantum computing, sensing, and control, deepening our grasp of the quantum world’s rich tapestry.
Beyond the immediate scope of photonics and condensed matter, this work might influence other fields such as acoustics, mechanics, and even biology, where wave-like phenomena in open and dissipative systems are ubiquitous. The conceptual framework and results presented here may inspire analogous studies in diverse domains, promoting cross-disciplinary fertilization and new technological breakthroughs.
In summary, Wang et al.’s groundbreaking exploration of coupled non-Hermitian skin effects intertwined with exceptional points represents a milestone in modern physics. Through rigorous theoretical modeling and insightful analysis, they reveal how the coupling of non-Hermitian lattices transcends simple additive behavior to create complex, hybrid modes characterized by unique localization and spectral features. Their findings chart a course toward sophisticated control of wave systems in open environments, paving the way for innovative devices with unprecedented functionalities rooted in the fascinating physics of non-Hermiticity.
As research in this vibrant field unfolds, we can anticipate rapid progress at the interfaces of mathematics, physics, and engineering, driven by insights such as those from this study. The convergence of non-Hermitian skin effects and exceptional points within coupled systems holds immense promise—not only for unlocking new physical laws but also for spawning technologies that harness the subtle art of wave manipulation in fundamentally new ways.
Subject of Research: Coupled non-Hermitian systems exhibiting skin effects and exceptional points
Article Title: Coupled non-Hermitian skin effect with exceptional points
Article References:
Wang, GH., Tao, R., Tian, ZN. et al. Coupled non-Hermitian skin effect with exceptional points. Light Sci Appl 14, 339 (2025). https://doi.org/10.1038/s41377-025-02006-6
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