Experimental observation of exceptional bound states in a classical circuit network

TL;DR

This paper reports the first experimental observation of exceptional bound states in a classical circuit network, demonstrating their robustness and potential for engineering stable modes in sensitive systems.

Contribution

It introduces the experimental realization of EB states in a classical circuit, bridging quantum phenomena with classical metamaterials.

Findings

EB states are robust and observable in classical circuits.

Spectral flow justifies the EB nature of lattice systems.

Stable resonant voltage profiles indicate successful realization.

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.