Just weeks after Microsoft showed off Majorana 2, a quantum chip it called 1,000 times more reliable than its predecessor and a major step toward practical quantum computing by 2029, a prominent researcher is openly disputing those claims.
In a commentary published Wednesday in Nature, University of St Andrews physicist Henry Legg argued that Microsoft has not demonstrated the existence of a topological qubit, a theoretical kind of quantum bit thought to be more resistant to errors than conventional quantum computing approaches.
'Not even the basic physics'
“My critique exposing flawed tune-up procedures, code errors, and omitted data behind Microsoft's 'breakthrough' quantum computing claims is published today in Nature,” Legg wrote on BlueSky. “In short: Microsoft haven't demonstrated the basic physics needed for even a single topological qubit.”
Legg's commentary responds to a 2025 paper published in Nature by Microsoft Quantum researchers that described evidence for the company's topological qubit. As Legg sees it, the signals Microsoft attributes to the device could instead simply be experimental noise.
“The detection of a topographical superconducting phase, the basis of proposed topological qubits, is notoriously difficult because trivial states can mimic the signatures expected from a topological superconductor,” Legg wrote.
What Microsoft claims for Majorana 2
Microsoft says Majorana 2 can keep quantum information stable for an average of 20 seconds, with some qubits lasting up to a minute. The company says AI helped speed up development by identifying promising materials, automating tests, and improving manufacturing. The chip relies on the very topological qubit technology critics are now questioning. Microsoft argues the approach could yield more reliable quantum computers by cutting down the errors that plague today's systems.
Legg contended that previously unpublished transport data behind Microsoft's results failed to show clear evidence of the superconducting state required to support the company's topological qubit claim. Instead, he said, the measurements looked more consistent with alternative explanations, including quantum dot effects.
Microsoft pushes back
Microsoft rejected Legg's conclusions. “We stand by our results and our roadmap,” Chetan Nayak, Microsoft's Technical Fellow and Corporate Vice President for Quantum Hardware, told Scientific American. Nayak pointed to Microsoft's advancement into the final phase of DARPA's Quantum Benchmarking Initiative, which he said followed independent evaluation of both public and proprietary results. “Skepticism and rigor are hallmarks of the scientific process, which we appreciate and have supported from various academics,” he added.
The company also published a formal response in Nature on Wednesday, arguing that its measurements support the conclusion that it has produced a topological qubit. Microsoft said the stable signals seen in its experiments are consistent with a topological state and would be unlikely to appear if the system were merely showing noise or behaving as a gapless state, as Legg suggests.
'Q-Day' and the risk to Bitcoin
The debate lands as the cryptocurrency industry races to prepare for “Q-Day,” the moment a quantum computer becomes powerful enough to break the public-key cryptography in wide use today.
Bitcoin is seen as especially vulnerable, because a quantum attacker could potentially derive private keys from exposed public keys and steal funds. Legg's critique does not rule out that future, but it does challenge the evidence Microsoft cites for getting there.
