Mapping and manipulation of topological singularities: from photonic graphene to T-graphene

TL;DR

This paper demonstrates the first theoretical and experimental mapping of topological singularities in a T-graphene lattice, revealing controlled topological charge conversion and pseudospin manipulation with potential applications in optical and quantum technologies.

Contribution

It introduces a novel T-graphene lattice with two coexisting topological singularities, enabling controlled topological charge conversion and manipulation of vortices.

Findings

Successful experimental demonstration of TS mapping in T-graphene

Controlled topological charge conversion between different TSs

Manipulation of vortices and high-order topological structures

Abstract

Topological singularities (TSs) in momentum space give rise to intriguing fundamental phenomena as well as unusual material properties, attracting a great deal of interest in the past decade. Recently, we have demonstrated universal momentum-to-real-space mapping of TSs and pseudospin angular momentum conversion using photonic honeycomb (graphene-like) and Lieb lattices. Such mapping arises from the Berry phase encircling the Dirac or Dirac-like cones, and is thus of topological origin. In this paper, we briefly present previous observations of topological charge conversion, and then we present our first theoretical analysis and experimental demonstration of TS mapping in a new T-graphene lattice. Unlike other lattices, there are two coexisting but distinct TSs located at different high-symmetry points in the first Brillouin zone of T-graphene, which enables controlled topological charge conversion in the same lattice. We show active manipulation of the TS mapping, turning the two TSs into vortices of different helicities, or one into a high-order vortex but the other into a quadrupole. Such TS manipulation and pseudospin-to-orbital conversion may find applications in optical communications and quantum information, and may bring insight into the study of other Dirac-like structures with multiple TSs beyond the 2D photonic platform.