Paraxial spin–orbit interactions as a resource for spin-hall effects and information engines

In this talk, we explore spin–orbit coupling in paraxial light as a resource for realising spin Hall effects within the paraxial regime and for controlling the flow of (quantum) information in optical systems. First, we show how the Pancharatnam topological index of vectorial beams underpins the emergence of chirality in vectorial optical fields. By controlling phase singularities in linearly and inhomogeneously polarised beams, we show that optical topology governs spin–orbit interactions, leading to light fields with tunable local spin characteristics. A direct consequence of this control is the manifestation of the spin Hall effect of light in the paraxial regime - previously believed to occur only in nonparaxial conditions or through light–matter interactions in anisotropic media. Subsequently, we demonstrate how spin–orbit coupling in paraxial light fields can be exploited to sort and control orbital angular momentum (OAM) states, using spin as an information handle or knob to emulate the behaviour of an agent that is capable of reducing the entropy of a physical system, the so-called Maxwell demon. This mechanism establishes a direct link between spin control and OAM manipulation, revealing how structured light can be used to implement information-driven optical processes analogous to thermodynamic feedback.