AUTHOR=Saito Shinichi 

TITLE=Topological polarisation states

JOURNAL=Frontiers in Physics

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2023.1225462

DOI=10.3389/fphy.2023.1225462

ISSN=2296-424X

ABSTRACT=Polarisation states are described by spin expectation values, known as Stokes parameters, whose trajectories in a rotationally symmetric system form a sphere named after Poincar é.Here, we show that the trajectories of broken rotational symmetric systems can exhibit distinct topological structures in polarisation states. We use a phase-shifter to form a polarisation circle (S 1 ), which interferes with the original input due to the phase change of the output state upon the rotation. By rotating the circle using a rotator, the trajectories become a polarisation torus (S 1 × S 1 ), which was experimentally confirmed in a simple set-up using passive optical components together with Mach-Zehnder interferometers. We also discuss about realisations of other topological features, such as a M öbius strip, a trefoil knot, Hopf-links, and topological Dirac bosons with a bulk-edge correspondence.