Quantum skyrmions outlast entanglement, hinting at more resilient networks

Quantum skyrmions outlast entanglement, hinting at more resilient networks Gaby Clark Scientific Editor Robert Egan Senior Editor Quantum networks could one day connect quantum computers into more powerful systems and enable new forms of secure communication. But a fundamental obstacle stands in the way: Quantum information is extraordinarily fragile, and the entanglement between particles of light on which such networks would depend is easily disrupted. Now, in a new paper in Nature Physics, engineers at the University of Pennsylvania have demonstrated a potential workaround using topology, the branch of mathematics that famously considers a doughnut and a coffee mug equivalent because they both have a single hole that remains unchanged even when their shapes are distorted. To explore whether topology's focus on properties that persist under deformation could lend resilience to quantum systems, the researchers built a chip that generates a pair of entangled photons, then gives one of them a distinctive pattern, known as a skyrmion, by polarizing its light in a particular way. The researchers found that they could transfer the skyrmion's pattern engraved on a single photon locally to the quantum state shared by the two photons remotely. Even more surprisingly, when the researchers introduced enough disruption to sever the photons' entanglement, the topological property remained intact. "It's as if one dancer's unique movement suddenly became part of a duet, and persisted even when the dancers were separated," says Liang Feng, professor in materials science and engineering (MSE) with a secondary appointment in electrical and systems engineering (ESE) and the paper's senior author. "If we can learn to encode information in such resilient patterns, that could lay the groundwork for much more reliable quantum networks." The topology of quantum skyrmions Unlike the hole in a doughnut, the defining topological feature of a quantum skyrmion isn't its physical shape, but a pattern in how its light is polarized. "The light oscillates in different directions depending on where you inspect it," says Haoqi Zhao, a postdoctoral fellow at Yale, alumnus of Feng's lab and the paper's first author. "It's sort of like how regions of hair on your head grow in different directions." In a quantum skyrmion, those variations form a pattern that encompasses all possible polarization states a fixed number of times. Even when individual parts of the pattern are disturbed, that number remains unchanged. "Think of a swirl in someone's hair," says Zhao. "You can push individual strands out of place without changing the overall pattern." Building a factory for quantum skyrmions Prior work by other researchers has shown how to create these patterns involving individual photons, as well as skyrmions shared between entangled photons. But no other team has demonstrated how to transfer a skyrmion's topological properties from a single photon to a quantum state shared by two photons, much less on the kind of small, scalable chip that could prove crucial to future quantum networks. Nearly half a decade of refining techniques went into the chip's development, with the team fabricating prototypes in Penn's Singh Center for Nanotechnology. "It's a bit like building an entire factory in miniature," says Yichi Zhang, a doctoral student in MSE and co-author of the paper. "One part of the chip generates entangled photons, another directs them where they need to go and still another creates the skyrmion pattern. The challenge was getting all the parts to work together." Unexpected results Once they had a working chip, the researchers deliberately introduced increasingly strong disturbances to the entangled photons they created, including unwanted background light. As the interference increased, measurements showed that the quantum state deteriorated and the photons' entanglement eventually disappeared. But the skyrmion's defining topological property remained intact, only breaking down under still stronger disruption. "Previous work suggested that these structures depended on entanglement," says Zhao. "Our findings show that the relationship is more complicated than we thought." New possibilities, new questions Beyond suggesting new ways to protect information in future quantum networks, the results also shed new light on the fundamental relationship between topology and quantum entanglement. Even after entanglement disappeared, certain quantum correlations persisted, as indicated by a measure known as "quantum discord," suggesting a broader connection between more general forms of quantum correlations and topology. "We've shown that these patterns can survive without entanglement, revealing a deeper role of quantum correlations beyond entanglement in quantum information processing," says Feng. "This discovery could not only deepen our understanding of quantum physics, but also help us develop new ways to protect quantum information." Publication details Haoqi Zhao et al., Chip-mediated manipulation of photonic quantum skyrmions, Nature Physics (2026). DOI: 10.1038/s41567-026-03487-x Journal information: Nature Physics Key concepts Conformation & topologyQuantum communication, protocols & technologyQuantum correlations, foundations & formalismProvided by University of Pennsylvania