Midway Evaluation in Physics - Valtýr Kári Daníelsson

Title of thesis:
Interacting polariton condensates in aperiodic lattices

Student:
Valtýr Kári Daníelsson

Doctoral committee:
Dr. Helgi Sigurðsson, reseach specialist at Science Institute, University of Iceland
Dr. Snorri Þ. Ingvarsson, professor at Faculty of Physics, University of Iceland
Dr. Michał Matuszewski, professor at Polish Academy of Sciences, Poland

Abstract:
In the recent years substantial effort has been dedicated towards exploring the nonequilibrium dynamics of coupled exciton-polariton condensates in novel two dimensional systems ranging from planar cavities, waveguides, and photonic crystals. Due to their high nonlinear response and competition over mutual gain these polariton condensates can lead to fascinating emergent behaviours and patterns when arranged into complex geometries. One of the topics is the properties of a polariton condensate in two dimensional quasicrystalline artificial optical lattices. Thereof, research was conducted in cooperation with experimental physicists on polariton condensates arranged in a P3 Penrose lattice followed by analysis on the properties of polariton condensates arranged in a novel aperiodic "einstein" monotile lattice. Our study is the first to explore polariton condensation in both Penrose and einstein quasicrystals. Another topic is the interaction between two ring-shaped polariton condensates in distinct optical traps, conducted also in cooperation with experimental physicists. This study examines different kinds of bonds that the condensates can form, which are analogous to sigma and pi bonds observed between p-orbitals. In addition to showing the existence of these states, we also describe the conditions under which they are stable and extend these findings to larger networks where we observe unusual emergent order remniscent of Ising and XY spin order.