Particles protected by Braids and Knots
We present a class of systems in which a particle - antiparticle pair cannot annihilate each other after they have moved along a loop, and instead form a new type of composite particle. This occurs in so-called non-Hermitian systems; classical metamaterials or "open" quantum systems that are coupled to the rest of the universe. Lukas Königis a PhD Student at Fysikum and is part of the research group Quantum and Complex Systems.
In two dimensions, their excitations are massless "particles" that can be created as a pair, or annihilate each other pairwise. Each particle is associated with the mathematical structure of a knot in a rope. After moving one particle along a loop, and bringing it near its former antiparticle, their knots are combined differently. The two can no longer annihilate pairwise and instead form a new particle corresponding to a more complicated knot. This shows that non-Hermitian particles in two dimensions remember their movement history.
More information
Braid-protected topological band structures with unpaired exceptional points
Last updated: October 18, 2023
Source: Fysikum