Laser beams carrying skyrmion numbers of 1, 2 and 3 crossed a 270-metre free-space optical link through central Johannesburg — and the encoded topology survived intact even when atmospheric turbulence scrambled the beam's polarization beyond recognition. That is the headline result from the Structured Light Lab at the University of the Witwatersrand (Wits), published in two studies, one in classical optics (Science Advances) and one in quantum optics (Physical Review Letters).

For R&D managers tracking free-space optical (FSO) communication and quantum networking, the finding addresses a persistent budget line: atmospheric turbulence correction. Current approaches lean on adaptive optics hardware or computationally expensive post-processing algorithms to undo distortions before or after transmission. Andrew Forbes, who heads the Wits lab, frames the alternative as encoding information in a property of light that turbulence cannot easily destroy — its topology.

How the encoding works. Skyrmions are knot-like, two-dimensional quasiparticle structures first observed in magnetic materials and more recently seen in electromagnetic fields and the electric field of light. The Wits team creates them by twisting the polarization or spin vectors of light in space so that every polarization appears exactly once, twice, three times and so on; the count is the skyrmion number. Because skyrmions are topologically stable, external perturbations leave the number unchanged.

The classical experiment. Forbes and colleagues shaped 532 nm laser light into vectorial beams using a spatial light modulator and a modified Mach–Zehnder interferometer, generating optical skyrmions with skyrmion numbers of 1, 2 and 3. They transmitted the beams across a real-world link on Wits' Braamfontein campus and measured the topology with a Stokes polarimetry setup. The skyrmion number held robust across a wide range of atmospheric conditions — from what Forbes describes as "calm, cool morning air to the highly erratic and intense distortions at midday."

"This result holds true even when the vectorial polarization of the underlying laser beam has been highly scrambled by atmospheric turbulence effects — and was therefore unrecognizable," Forbes says.

The quantum experiment. The second study built topology from in-built correlations between two photons entangled in their optical angular momentum (OAM). This matters because OAM quantum states are themselves unstable in distorting environments; the information they encode is easily lost. In a controlled laboratory environment with media at varying turbulence levels, a skyrmion with skyrmion number 1 maintained topological numbers close to 1 despite local distortions. The team concludes the topological number is fundamentally decoupled from turbulence-induced modal crosstalk and the spreading of an individual photon's OAM.

Despite the very different physical systems, both experiments point to the same conclusion, Forbes says: conventional properties of optical fields degrade sharply under distortion, while the topological information encoded in those states stays remarkably robust. Together, the two works demonstrate topology as an information carrier in both classical and quantum systems across distinct communication and information-processing scenarios.

Caveats worth noting. No physical protection mechanism guarantees optical robustness the way an energy barrier protects topology in condensed matter systems. Optical topologies are easy to create and manipulate, but their resilience had to be tested empirically — which is precisely what motivated the work. "We therefore wanted to address a fundamental question: how robust is optical topology when light encounters a real-world, highly distorting environment?" Forbes says.

The team also confronted two practical hurdles that any replication effort should anticipate. First, precision optics outdoors: sunlight and temperature shifts, wind, rain, and even thermal expansion of buildings threatened optical alignment and long-duration measurement stability. Second, metrology: existing methods for measuring optical topology are sensitive to noise and experimental imperfections, forcing the researchers to develop new data acquisition and processing methods to separate genuine channel changes from artifacts of the measurement process itself.

Portfolio implications. Forbes identifies free-space optical, satellite and space communications as applications, along with links to remote or underserved communities where turbulence and missing infrastructure constrain deployment. The quantum result carries a further implication for quantum network architecture: "We know that entanglement decays in real-world conditions that are not pristine. Our work shows that despite this, the quantum information stored in the topology remains intact. This may allow us to distribute information across a quantum network in a more reliable and robust manner," he says. Beyond communications, the team sees the robustness extending to optical sensing and information processing in complex or noisy environments.

The immediate next steps are concrete: testing whether the observed robustness extends to underwater channels and biological tissue, where scattering and birefringence are far more prevalent than in air; developing dedicated detectors and measurement techniques for optical topology; and running high-speed communication experiments with realistic protocols to quantify how much information a "topological alphabet" can reliably transmit.