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A top quantum computing expert assails Microsoft’s claims that it has a “topological qubit,” arguing in a new paper that the company has failed to demonstrate the technology.

University of St Andrews physicist Henry Legg argues that the “topological qubit,” a storer of quantum information that could theoretically maintain a higher fidelity than any in existence, might simply be noise.

The commentary was published today in Nature’s “Matters Arising,” the journal’s venue for formal criticism of its published papers. Legg’s response is aimed at Microsoft’s most recent Nature paper, which was published earlier this month—but it is just the latest in a string of criticism aimed at Microsoft’s Quantum division by other researchers in the field.

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The company has been forced to retract certain previous peer-reviewed papers. And in the new commentary, Legg argues that their most recent Nature paper may be similarly flawed. In a response also published today by Nature, a member of Microsoft’s Quantum team argues that their measurements do justify the claim that they’ve produced a topological qubit.

In a statement to Scientific American, Microsoft’s Technical Fellow and Corporate Vice President, Quantum Hardware, Chetan Nayak said, “We stand by our results and our roadmap. At the end of the day, success is the delivery of a scalable quantum computer. We are confident in our ability to execute against our roadmap and proud of our continued engagement with DARPA, which moved Microsoft into the final phase of its Quantum Benchmarking Initiative after independently evaluating our results—those in the public realm and proprietary—with a team of highly qualified experts. Skepticism and rigor are hallmarks of the scientific process, which we appreciate and have supported from various academics. We have participated in dialogue and our thorough rebuttal was accepted and published by Nature.”

The critique—which Microsoft has known was in the works at Nature for some time—lands on the heels of the company’s unveiling of the “Majorana 2” chip, and an updated timeline to produce “scalable, practical quantum computing” to the end of the decade. “They simply cannot sell the 2029 roadmap as credible to the public when the underlying physics is not there,” Legg says.

“The ‘Matters Arising’ makes it painfully apparent that the paper in Nature has no scientific value,” says Sergey Frolov, a physicist at the University of Pittsburgh who was not involved in either paper. “And that it likely needs to be retracted, like the other Nature papers associated with Microsoft.”