Implementation and topological characterization of Weyl exceptional rings in quantum-mechanical systems

TL;DR

This paper reports the first quantum-mechanical realization of Weyl exceptional rings using a superconducting qubit and dissipative resonator, demonstrating their topological properties and transitions through eigenvector analysis.

Contribution

It introduces a novel quantum implementation of Weyl exceptional rings and explores their topological transitions, expanding understanding beyond classical wave systems.

Findings

Successful quantum implementation of Weyl exceptional rings

Measurement of quantized Berry phase and Chern number

Observation of topological transition by shrinking parameter space

Abstract

Non-Hermiticity can lead to the emergence of many intriguing phenomena that are absent in Hermitian systems, enabled by exceptional topological defects, among which Weyl exceptional rings (WER) are particularly interesting. The topology of a WER can be characterized by the quantized Berry phase and a nonzero Chern number, both encoded in the eigenvectors of the non-Hermitian Hamiltonian. So far, WERs have been realized with classical wave systems, whose eigenvectors can be well described by classical physics. We here report the first quantum-mechanical implementation of WERs and investigate the related topology transitions. The experiment system consists of a superconducting qubit and a dissipative resonator, coupled to each other. The high flexibility of the system enables us to characterize its eigenvectors on different manifolds of parameter space, each of which corresponds to a quantum-mechanical entangled state. We extract both the quantized Berry phase and Chern number from these eigenvectors, and demonstrate the topological transition triggered by shrinking the size of the manifold.