The work performed during the action followed three main lines of research. In the first part of the action, theoretical research was performed to clarify and properly define the concept of helicity for photons in inhomogeneous dispersive optical media. This work has broad implications for studying topological invariants in photonic systems and for investigating the interaction with chiral molecules and magneto-electric emitters.
Later, attention has been focused on theoretically demonstrating the nontrivial topological properties of bichromatic photonic crystals by means of extensive numerical simulations. The nontrivial topology of the optical spectrum of bichromatic structures is illustrated by the formation of topologically protected, strongly localized boundary states when a finite-size extent of the bichromatic photonic crystal is embedded in a larger structure. Interestingly, these boundary states reveal a deep connection with condensed matter physics, since it can be proved that they are equivalent to the topologically-protected edge states of the integer quantum Hall effect.
Finally, the third line of research aims at creating a collaborative theoretical-experimental environment. In order to do this, the Fellow has been actively involved in several experimental projects with other members of the hosting Institution, resulting in joint theoretical-experimental work on topological systems in photonics. This collaboration led to the demonstration of a chiral interface based on the coupling between the local spin of light and the valley degree of freedom of two-dimensional excitons in transition-metal-dichalcogenide monolayers and the investigation of the properties of topological points (phase and polarization singularities) in random light fields.
In general, the results of the action have been extremely satisfactory and even exceeding the expectations of the research proposal. The findings have been the subject of several scientific articles in top international journals (6 articles in journals with impact factor > 7). Moreover, they have been presented at three international conferences and several workshops and meetings.
