Topological robustness of optical skyrmions through a real-world free-space link.

Structured light offers a promising solution for the increasing data demands of modern optical networks, opening up degrees of freedom that can be leveraged for greater channel capacity and more bits per photon. However, its implementation is hindered by real-world distortions, for example, atmospheric turbulence in free space, with severe and rapidly evolving phase perturbations that alter the amplitude, phase, and vectorial polarization structure of the beam. Here, we demonstrate that optical topologies in the form of skyrmions are highly resilient to the effects of real-world atmospheric turbulence. We create and transmit these particle-like topologies of light through a 270-meter free-space optical link, revealing their robustness across a wide variety of conditions and turbulence strengths. While we observe severe distortion in the states' underlying degrees of freedom, we show that the topological numbers are preserved in all cases. We account for fast changes to the medium, where the channel produces statistically averaged outcomes, by probing the state's decoherence, showing that while the degree of polarization consequently decays, the topology remains intact. Using topology, we show that information can be transmitted through the channel with almost perfect fidelity (>98%) in most cases, only decreasing to 86% in the most severe conditions tested. This work idemonstrates the potential for optical topologies as reliable and robust information carriers in a real-world environment and points to the potential for other complex channels too, offering attractive features for classical and quantum communication alike.