Polarisation singularities in photonic crystals for an on-chip spin-photon interface

We demonstrate a photonic crystal waveguide design that supports polarisation singularities - positions in the electric field vector where one of the parameters describing the local polarisation ellipse is singular. We show how these singularities can be used to transfer quantum information between the spin states of an electron in a quantum dot and the path of a photon in the photonic crystal waveguide.