Measuring Electromagnetic and Gravitational Responses of Photonic Landau Levels

Understand

The topology of an object describes global properties that are insensitive to local perturbations.

• Classic examples include string knots and the genus (number of handles) of a surface: no manipulation of a closed string short of cutting it changes its "knottedness"; and no deformation of a closed surface, short of puncturing it, changes how many handles it has.
• Topology has recently become an intense focus of condensed matter physics, where it arises in the context of the quantum Hall effect [1] and topological insulators [2].
• In each case, topology is defined through invariants of the material's bulk [3-5], but experimentally measured through chiral/helical properties of the material's edges.