Summary
- Physicist Henry Legg contends that Microsoft has not proven the existence of a topological qubit.
- This critique specifically addresses the technology behind Microsoft's recently introduced Majorana 2 chip.
- Microsoft has refuted these claims, providing a defense of its findings in an official statement.
Following Microsoft's announcement of the Majorana 2 chip, which the company claimed is 1,000 times more reliable than its predecessor and a significant advancement toward practical quantum computing by 2029, a prominent researcher is disputing the company's assertions.
In a commentary released on Wednesday in Nature, physicist Henry Legg from the University of St Andrews stated that Microsoft has not successfully demonstrated a topological qubit, a theoretical quantum bit that could offer better error resistance compared to traditional quantum computing methods.
Legg mentioned on BlueSky, “My critique exposing flawed tune-up procedures, code errors, and omitted data behind Microsoft's 'breakthrough’ quantum computing claims is published today in Nature. In short: Microsoft hasn't demonstrated the basic physics needed for even a single topological qubit.”
This commentary counters a 2025 paper by Microsoft Quantum researchers that claimed evidence for the existence of a topological qubit. Legg argues that the signals Microsoft claims to have detected could actually be experimental noise.
“Detecting a topological superconducting phase, which is fundamental to proposed topological qubits, is notoriously challenging, as trivial states can mimic the expected signatures of a topological superconductor,” Legg elaborated.
Microsoft asserts that its Majorana 2 chip can maintain quantum information stability for an average of 20 seconds, with some qubits potentially lasting up to a minute. The company claims that AI has accelerated development by identifying promising materials, automating testing processes, and enhancing manufacturing capabilities. The chip relies on the same topological qubit technology that is currently under scrutiny from critics. Microsoft maintains that this approach could yield more dependable quantum computers by minimizing errors prevalent in current systems.
Legg contended that previously unreleased transport data supporting Microsoft's findings did not provide clear evidence of the superconducting state necessary for the company's topological qubit claim. Instead, he suggested that the measurements seemed more aligned with alternative explanations, such as quantum dot effects.
In response to Legg's assertions, Microsoft defended its position.
"We stand by our results and our roadmap," stated Chetan Nayak, Microsoft's Technical Fellow and Corporate Vice President for Quantum Hardware, in an interview with Scientific American. Nayak highlighted Microsoft's progress within the final phase of DARPA's Quantum Benchmarking Initiative, which he claimed underwent independent evaluation of both public and proprietary data. “Skepticism and rigor are essential to the scientific process, which we appreciate and have supported from various academics,” he noted.
Microsoft also published a formal response in Nature on Wednesday, asserting that its measurements substantiate the conclusion that it has achieved a topological qubit. The company argued that the stable signals observed during its experiments align with a topological state and would be unlikely to occur if the system was merely exhibiting noise or acting as a gapless state, as suggested by Legg.
This discussion arises as the cryptocurrency sector prepares for "Q-Day," the moment when a quantum computer becomes powerful enough to compromise widely used public-key cryptography.
Bitcoin is seen as particularly at risk since a quantum adversary could potentially derive private keys from exposed public keys, jeopardizing funds. Although Legg's critique does not dismiss this future possibility, it does question the evidence Microsoft presents to support its claims.