Simulating Exceptional Non-Hermitian Metals with Single-Photon Interferometry

TL;DR

This paper demonstrates the experimental simulation of non-Hermitian metals with complex topological features using single-photon interferometry, revealing new insights into exceptional lines and their symmetry-dependent properties.

Contribution

It introduces a photonic method to simulate and analyze the topology of non-Hermitian metals, including symmetry-protected and knot-like exceptional lines.

Findings

Observation of symmetry-protected exceptional lines in 2D systems.

Identification of knot-like exceptional lines in 3D systems.

Analysis of how symmetry-breaking affects exceptional line topology.

Abstract

We experimentally simulate in a photonic setting non-Hermitian (NH) metals characterized by the topological properties of their nodal band structures. Implementing nonunitary time evolution in reciprocal space followed by interferometric measurements, we probe the complex eigenenergies of the corresponding NH Bloch Hamiltonians, and study in detail the topology of their exceptional lines (ELs), the NH counterpart of nodal lines in Hermitian systems. We focus on two distinct types of NH metals: two-dimensional systems with symmetry-protected ELs, and three-dimensional systems possessing symmetry-independent topological ELs in the form of knots. While both types feature open Fermi surfaces, we experimentally observe their distinctions by analyzing the impact of symmetry-breaking perturbations on the topology of ELs.