Metanano 2021

Last week I attended the virtual Metanano 2021 conference and presented an invited talk in the "Topological states in classical and quantum systems" session. Here are my talk slides. The conference organisers have kindly made the session recordings available on YouTube until 3rd October (link to schedule of talks).

The topological session allowed me to catch up on some recent developments in topological photonics that I haven't had time to closely follow. Highlights from the Thursday session I attended:

Baile Zhang reported on the observation of antichiral edge states using microwave gyromagnetic photonic crystals. In conventional topological photonic crystals, the chiral states on opposite edges propagate in opposite directions, ensuring local conservation of energy. A 2018 PRL paper showed how to design antichiral edge states that propagate in the same direction on both edges, with energy conservation provided by counter-propagating bulk modes. The antichiral edge states do not support topologically-protected transport (since they do not reside in a complete band gap), but they are nevertheless interesting as a means of extending the possibilities offered by chiral edge states.

Yidong Chong discussed topological defect states in photonic and acoustic lattices. By introducing defects such as dislocations and disclinations into the bulk of topological photonic crystals, one can create free-form waveguides with near-arbitrary trajectories. This enables the flexible creation of topological analogues of regular photonic crystal waveguides. Extending to 3D structures enables the design of topological waveguides for orbital angular momentum modes, with the propagation direction controlled by the handedness of the mode vorticity.

Jian-Hua Jiang reported on a closely related idea - the experimental observation of bulk-disclination correspondence in topological crystalline insulators. What's really interesting about this work is that bulk topological defects can be sensitive to exotic topological invariants (e.g. higher order topological phases associated with fractional charge modes) that cannot be distinguished using the more familiar bulk-edge correspondence. He also mentioned a recent preprint on multi-band topological pumping using magnetic defects in acoustic metamaterials.

Daniel Sievenpiper presented recent work on coupling light between topological and non-topological photonic crystal waveguides, and using terminations of topological waveguides to create collimated far-field radiation. This opens avenues in the direction of topological antennas.

There are other interesting-sounding talks that I missed due to other commitments and time zone differences that I hope to catch up on while the recordings are available.