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

Localization phenomena during transport are typically driven by disordered scalar potentials. Here, we predict a universal pseudospin localization phenomenon induced by a disordered vectorial potential and demonstrate it experimentally in an optical analogue of a classical disordered spin-glass magnetic phase. In our system, a transverse disorder in the second-order nonlinear coupling of a nonlinear photonic crystal causes the idler-signal light beam, representing the pseudospin current, to become localized in the transverse plane. This effect depends strongly on the nonlinear coupling strength, controlled by the optical pump power, revealing its inherently nonlinear and non-perturbative 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 deep insights into spin transport in disordered magnetic textures and open avenues for exploring complex magnetic phases and phase transitions using nonlinear optics.