Topological polariton states in photonic lattices

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Recent advances in semiconductor nano-technology have led to a new generation of robust controllable structures where manipulation of coupling between light and matter can be performed on a sub-micrometer scale. In these structures novel quasiparticles - polaritons - which are a mixture of light and matter (excitons) can be created. Polaritons have a very small effective mass, and thus may condense in a single quantum state at high temperatures. This macroscopically occupied state has properties similar to those of atomic Bose-Einstein condensates. In addition, while photons propagating in free space do not interact, the matter component in the polariton wavefunction enables strong inter-particle interactions. This nonlinearity gives rise to rich phenomena ranging from superfluidity of light, ultra-low power self-localised wavepackets (solitons) to generation of single photons and entangled photon pairs. This project concerns the investigation of polaritons in lattices of coupled zero-dimensional microresonators, where the combined effects of the lattice periodic potential, the coupling between spin and orbital degrees of freedom and applied magnetic field allow topological effects from condensed matter physics to be studied using polariton quasiparticles (bosons of zero charge). A particular emphasis on this project will be placed on the study of topologically protected edge states at the boundaries of these lattices, and the effects of gain, loss and nonlinearity on the polariton topology.