Fractional Vortices Observed in Superconductor After 24-Year Theory

For twenty-four years, Egor Babaev's theory sat in a drawer. Superconductors could host fractional vortices — not the standard integer-flux kind, but partial ones, splitting what should be whole. It was beautiful mathematics. Nobody could find one.

The experimental vindication arrived May 21, 2026, in Science. Babaev, now at KTH Royal Institute of Technology in Sweden, appears as a co-author alongside Hong Ding's team at Shanghai Jiao Tong University's Tsung-Dao Lee Institute, Kathryn Moler's group at Stanford, and their collaborators. The paper shows what Babaev predicted in 2002: in a multiband superconductor called KFe2As2, integer vortices can split into fractional ones. At 4.2 Kelvin, some vortices branch into two cores, others into three, and recombine as temperature drops. These fractional vortices arrange in chains that form chiral skyrmions — topological structures characterized by a CP2 invariant, meaning they carry a protected mathematical charge that is robust against continuous deformations.

The finding lands alongside an independent Nature paper, also published this week, on a different platform: granular aluminum thin films near the superconductor-insulator transition. That work, from a team at the Karlsruhe Institute of Technology, showed that the same disorder engineers have spent decades fighting in superconducting circuits can generate stable two-level quantum states through quantum tunneling. Both papers cite Babaev's 2002 proposal. Neither refers to the other. The physics arrived twice, in two different material systems, within days of each other.

The broader pattern is what makes this worth sitting with. Quantum computing hardware has, for twenty years, been built on a single principle: eliminate disorder. Josephson junction qubits require pristine aluminum films, crystalline substrates, and extraordinary isolation from magnetic interference. Vortices are public enemy number one. They nucleate where material defects live, ruin coherence times, and limit how large a superconducting chip can get before its performance collapses.

The vortex result suggests that decades of received wisdom ran the problem backward. Babaev has argued in published work that disorder-tolerant design is not a compromise but an architecture — the goal is not to eliminate imperfection but to build around it. Granular aluminum near the superconductor-insulator transition self-assembles into exactly the nanostructure needed; no clean-room precision required. KFe2As2's fractional vortices emerge from broken time-reversal symmetry in a multiband superconductor, requiring no fine-tuned crystal growth. In both cases, the imperfection is the feature.

A separate lineage runs the same philosophy in a different material system. Nitrogen-vacancy centers in diamond are lattice vacancies — atomic-scale defects — that act as natural spin qubits. Rather than building an artificial atom from scratch, the NV center is a defect that nature already provides; the field's decades of work went into learning to control it rather than eliminate it. Microsoft's Majorana-based topological qubits pursue a different version of the same inversion: the protection is intrinsic to the topology, not imposed from outside. Topological qubits in general are built on the principle that quantum information is protected by symmetry rather than isolated from it. The pattern extends beyond superconductors.

That is a different philosophy from where the field has been. Whether it scales is an open question. Both papers demonstrate existence. Neither demonstrates coherent control, gate fidelity, or a path to the millikelvin operating temperatures of a real quantum computer. The Science paper's vortices are thermal excitations at 4.2 Kelvin; operational superconducting qubits live around 15 millikelvin. Babaev's 2002 paper noted the potential relevance to topological quantum computation, but that connection remains theoretical, not demonstrated. One senior researcher in the superconducting qubit field, reached for comment, said the history of the field is littered with material platforms that worked beautifully in isolation and collapsed when anyone tried to scale them — and that Josephson junction technology has a twenty-year head start and entrenched manufacturing infrastructure behind it. The practical path from lab curiosity to manufacturable qubit is uncharted, and the people most cautious about timelines are usually the ones closest to the hardware.

What the twin publications suggest, at minimum, is that the phenomenon is general. When two independent platforms produce the same unexpected physics in the same week, it is usually not a coincidence — it is a category. Fractional vortices and disorder-tolerant superconducting states appear to be a class of quantum behavior, not a single material's quirk. That narrows the space of what has to be true for the result to matter.

An earlier 2023 paper by Iguchi, Babaev, and Moler, published in Science, had already confirmed fractional flux vortices existed in the same material using a SQUID at Stanford — that was the first experimental glimpse. The new result is the direct imaging of core fractionalization that makes the mechanism undeniable. Babaev and Moler have the coherence and gate fidelity data they declined to share ahead of publication; the community will know when they publish it.

The raw data and analysis code are already on Zenodo, published the same day as the paper. Until then, the honest version of this story is: a 24-year-old theory just got its first confirmed experimental footing, two different ways, in one week. What it becomes next is an engineering problem that has barely started.