Observation of Discrete 1D Solitons in an Optically Induced Lattice in Rubidium Atomic Vapor

The manipulation of light in periodic structures is fundamental to the development of discrete photonics and provides a versatile platform for controlling light propagation in integrated and quantum photonic systems. This work reports the experimental observation of discrete one-dimensional (1D) solitons in a photonic lattice, optically induced in warm rubidium vapor. The lattice is generated by the interference of two coupling laser fields intersecting at a small angle, which creates a spatially modulated 1D refractive index. When a probe beam is focused into a single lattice site, discrete diffraction is observed. By increasing the probe intensity, discrete solitons emerge as a result of the balance between discrete diffraction and self-focusing within the nonlinear atomic medium. Experimental results are supported by numerical simulations, in which the refractive index is modeled via optical Bloch equations for a multilevel atomic system driven by the coupling and probe fields in a $Λ$ configuration. These results, combined with the inherent controlability of gain and loss in atomic vapors, suggest that this platform provides a versatile foundation for exploring non-Hermitian nonlinear dynamics and parity-time-symmetric photonic lattices.