Fig. 2: Experimental demonstration of the edge state at the zigzag edge.

a Interference pattern of three coupling beams creating the lattice with a lattice constant of \(112\,\upmu {\mathrm{m}}\). This hexagonal lattice induces the honeycomb lattice in Fig. 1e under EIT conditions. The edge marked by the dotted line corresponds to zigzag edge. b The incident stripe probe beam. Scale bar: 200 μm. c The edge state excited by the probe beam at \(\Delta _1 = 135\,{\mathrm{MHz}}\) with the probe power being \(100\,\upmu {\mathrm{W}}\). d Diffraction of the probe beam into the bulk of the lattice at \(\Delta _1 = 105\,{\mathrm{MHz}}\). e Interference pattern of the output probe beam from panel c with a reference beam illustrating staggered phase of the edge state. a–e share the same scale bar defined in (b). f Theoretical interference pattern calculated for extended linear edge state. g, h Output probe beams for different temperatures (effectively corresponding to different propagation distances) at \(\Delta _1 = 135\,{\mathrm{MHz}}\) revealing motion of the edge state. White lines at the bottom show intensity profiles of the probe beam along the dashed lines. Considering the absorptive nature of atomic medium, the linear gain \(g\) (which only affects the visibility, but not the profile of the beams) of the CCD camera is used to improve the appearance of figures. The CCD gain for (g) and (h) are \(g = 0\) (no gain) and \(g = 8\), respectively. Scale bar: 200 μm.