Experimental observation of exceptional bound states in a classical circuit network

Abstract

Exceptional bound (EB) states represent an unique new class of robust bound states protected by the defectiveness of non-Hermitian exceptional points. Conceptually distinct from the more well-known topological states and non-Hermitian skin states, they were recently discovered as a novel source of negative entanglement entropy in the quantum entanglement context. Yet, EB states have been physically elusive, being originally interpreted as negative probability eigenstates of the propagator of non-Hermitian Fermi gases. In this work, we show that EB states are in fact far more ubiquitous, also arising robustly in broad classes of systems whether classical or quantum. This hinges crucially on a newly-discovered spectral flow that rigorously justifies the EB nature of small candidate lattice systems. As a highlight, we present their first experimental realization through an electrical circuit, where they manifest as prominent stable resonant voltage profiles. Our work brings a hitherto elusive but fundamentally distinctive quantum phenomenon into the realm of classical metamaterials, and provides a novel pathway for the engineering of robust modes in otherwise sensitive systems.

14 pages, 8 figures

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• Engineering topological states and quantum-inspired information processing using classical circuits
• Quantum entanglement and non-Hermiticity in free-fermion systems
• Protected chaos in a topological lattice
• Thermodynamics and entanglement entropy of the non-Hermitian SSH model
• Non-Hermitian Skin Effect Along Hyperbolic Geodesics
• Entanglement Hamiltonian and effective temperature of non-Hermitian quantum spin ladders
• Nonlinear Hall effects with an exceptional ring
• Non-Hermitian entanglement dip from scaling-induced exceptional criticality
• Many-body critical non-Hermitian skin effect
• Fidelity and quantum geometry approach to Dirac exceptional points in diamond nitrogen-vacancy centers
• Interacting many-body non-Hermitian systems as Markov chains