Observation of pseudospin-locked chiral edge transport in gyromagnetic photonic crystals

Abstract

Photonic pseudospins enable selective excitation and routing of light, but perturbations that mix opposite pseudospins can induce backscattering in helical edge channels. Here, we experimentally demonstrate pseudospin-locked chiral edge transport in gyromagnetic photonic crystals, combining pseudospin selectivity with nonreciprocal unidirectional propagation. By jointly engineering lattice deformation and magnetic bias, we control dipolar-quadrupolar band inversions and construct interfaces supporting pseudospin-selective chiral channels. Microwave near-field and transmission measurements reveal a single chiral edge branch that is selectively excited by only one source handedness and exhibits pronounced nonreciprocal transport. Extending this mechanism to multidomain structures, we combine two pseudospin channels into a common waveguide, separate them into distinct outputs, and route them through intersecting interfaces. These configurations realize a nonreciprocal photonic pseudospin multiplexer and demultiplexer, together with a waveguide crossing exhibiting average measured crosstalk of -14.1 and -15.8 dB for its two input channels. Our results present an experimental route to integrating pseudospin-selective channel control with chiral edge transport, providing a foundation for nonreciprocal photonic networks that use pseudospin to organize and route multiple wave channels.