Physicist challenges Microsoft’s topological qubit claims.
Physicist Henry Legg from the University of St Andrews has questioned the conclusions of a Microsoft Azure Quantum paper dated February 19, 2025, which the company used to support its claims about the topological qubit. His commentary was published in Nature on June 24.
On the same day, the journal published a response from the corporation, which disagreed with the criticism.
A topological qubit is a type of quantum bit designed to be more error-resistant due to its method of storing information.
What Legg Disputed
Legg analyzed transport data from Microsoft’s 2025 work, which shows how current flows through an experimental device and helps determine if the system is in the desired quantum state.
According to Legg, the data does not confirm the presence of a stable superconducting gap in the areas where Microsoft conducted parity readings. The superconducting gap is crucial in this context because, without it, interpreting the measurements as topological is more challenging.
Legg believes the observed signals could have more conventional explanations, including quantum dot effects and device disorder. In simpler terms, he argues that Microsoft may have mistaken non-topological states for signs of the desired mode.
Microsoft’s Response
Microsoft rejected Legg’s conclusions. The authors stated that their measurements do not require the assumption of a gap, and the observed signals are consistent with a topological state. This position was supported by Microsoft’s Quantum Hardware technical lead, Chetan Nayak.
“We stand by our results and our roadmap,” he stated.
Nayak referred to Microsoft’s participation in the DARPA program. In February 2025, the agency selected Microsoft and PsiQuantum for the verification and co-design phase of US2QC. The agency describes this program as part of the broader Quantum Benchmarking Initiative, aimed at determining whether an industrially useful quantum computer can be built by 2033.
Why the Debate Involves Majorana 2
On June 2, 2026, Microsoft introduced Majorana 2, a new generation of topological quantum chips. According to the company, the average qubit lifetime reached 20 seconds, and in some cases, minutes.
The corporation also reported an operation speed of about 1 microsecond, a qubit size of approximately 0.01 mm, and a goal to create a scalable quantum computer by 2029. The company attributed the progress to replacing aluminum with lead in the superconducting layer and using Microsoft’s AI tools, Discovery.
Legg’s commentary is not a direct analysis of Majorana 2. It pertains to the 2025 paper on InAs–Al devices, related to Majorana 1. However, Decrypt noted that the debate touches on the technological foundation underlying Microsoft’s new roadmap.
Physicist Sergey Frolov from the University of Pittsburgh told Scientific American that Microsoft’s work in Nature likely needs to be retracted.
Earlier, in June, D-Wave Quantum unveiled a roadmap for the phased development of quantum systems. By 2032, the company plans to create a fault-tolerant quantum computer with 100 logical qubits.
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