Fig. 2: Experimental demonstration of topological conversion in a pseudospin-1/2 honeycomb lattice.
From: Universal momentum-to-real-space mapping of topological singularities
a Top: an optically induced HCL; Bottom: input pattern of vortex-bearing triangular lattice beam used for selective excitation of the pseudospin states. b–e Top (bottom) row corresponds to initial excitation of s = 1/2 (s = −1/2) pseudospin state with vortex beams of initial topological charge l = 1 (l = −1). Interferograms of input (b, c) and output (d, e) with a tilted reference beam showing topological charge conversion from 1 to 2 (top) and from −1 to −2 (bottom). b, d Interferogram from the whole beam, and (c, e) corresponding interferogram from one of the spectral components. Difference in the numbers of counted fringes from the two sides of the marked region illustrates the net topological charges at output in (d, e). White curved arrows mark the position and helicity of the vortices. Insets in (c) and (e) show singly and doubly-charged vortex intensity patterns obtained at input and output, respectively, from one of the K valleys as illustrated in Fig. 1a.
