Pseudospin Transverse Localization of Light in an Optical Disordered Spin-Glass Phase.

Localization phenomena during transport are typically associated with disordered scalar potentials. Here, we predict a universal pseudospin localization phenomenon driven by a disordered vectorial potential and experimentally observe its onset in an optical analog of a classical disordered spin-glass magnetic phase. In our system, disorder in the second-order nonlinear coupling of a nonlinear photonic crystal causes the idler-signal light beam, representing the pseudospin current, to approach localization in the transverse plane. This effect depends strongly on the nonlinear coupling strength, controlled by the optical pump power, revealing its inherently nonlinear nature. Furthermore, this phenomenon is marked by decaying Rabi oscillations between the idler and signal fields, linked to the disorder properties, suggesting an accompanied longitudinal decoherence effect. Our findings offer new insights into spin transport in disordered magnetic textures and open avenues for exploring complex magnetic phases and phase transitions using nonlinear optics.