# A Photonic Topological Mode Bound to a Vortex

## TL;DR

This paper demonstrates the experimental observation of a topological defect mode in a 2D photonic crystal with a vortex, revealing a zero-energy mode related to Majorana states, advancing understanding of topological photonics.

## Contribution

It introduces a novel experimental method to excite and observe topological defect modes in large-scale photonic crystals with vortex distortions.

## Key findings

- Observed a zero-energy topological mode at a vortex in a photonic crystal.
- First experimental demonstration of a Dirac equation solution with a vortex in photonics.
- Mode closely related to Majorana bound states in superconductors.

## Abstract

Topological photonics sheds light on some of the surprising phenomena seen in condensed matter physics that arise with the appearance of topological invariants. Optical waveguides provide a well-controlled platform to investigate effects that relate to different topological phases of matter, providing insight into phenomena such as topological insulators and superconductors by direct simulation of the states that are protected by the topology of the system. Here, we observe a mode associated with a topological defect in the bulk of a 2D photonic material by introducing a vortex distortion to an hexagonal lattice and analogous to graphene. These observations are made possible by advances in our experimental methods. We were able to manufacture uniform large two-dimensional photonic crystal structures, containing thousands of identical waveguides arranged in two dimensions, and we developed a new method to excite multiples of these waveguides with a well-defined light field. This allows us to probe the detailed spatial features of topological defect modes for the first time. The observed modes lie mid-gap at zero energy and are closely related to Majorana bound states in superconducting vortices. This is the first experimental demonstration of a mode that is a solution to the Dirac equation in the presence of a vortex, as proposed by Jackiw and Rossi.

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Source: https://tomesphere.com/paper/1901.04439