Persistent Spin Grids with a Spin-Orbit-Coupled 2D Electron Gas.

We consider the diffusive spin dynamics of a 2D electron gas with spin-orbit coupling confined within a grid of narrow channels. We show that the lifetime of certain spin distributions in such grids greatly exceeds that in an unconfined 2D electron gas and diverges as the channel width approaches zero. Such persistent spin grids are akin to spin crystals and occur if the electron spin orientation remains invariant after diffusion around the grid plaquette. We establish a topological Z_{2} classification for persistent spin grids and show how the grids with spatially varying parameters can simulate non-Abelian lattice gauge theories.