Physicist Henry Legg from the University of St Andrews has questioned the conclusions of a February 19, 2025 article by Microsoft Azure Quantum, which the company used to support some of its claims about the topological qubit. His comments were published on June 24 in Nature.
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 resistant to errors due to its method of storing information.
What Legg Challenged
The physicist analyzed transport data from Microsoft’s 2025 work. This data shows how current flows through an experimental device and helps determine whether the system is in the correct quantum state.
According to Legg, the data does not support the existence of a stable superconducting gap in the areas where Microsoft conducted parity readouts. The superconducting gap is crucial in this context because, without it, it is harder to justify interpreting the measurements as topological.
Legg believes that the observed signals might have more conventional explanations, including effects from quantum dots and disorder in the device. In simpler terms, he argues that Microsoft may have mistaken non-topological states for signs of the desired regime.
Microsoft's Response
Microsoft rejected Legg’s conclusions. The authors stated that their measurements do not require a prior assumption of a gap, and the observed signals are consistent with a topological state. This position was supported by Chetan Nayak, the technical lead for Microsoft Quantum Hardware.
“We stand by our results and our roadmap,” he stated.
Nayak referenced Microsoft’s involvement in a DARPA program. In February 2025, the agency selected Microsoft and PsiQuantum for a verification and co-design phase under US2QC. The agency describes this program as part of a broader Quantum Benchmarking Initiative aimed at assessing whether a commercially viable quantum computer can be developed by 2033.
Why the Dispute Relates to Majorana 2
On June 2, 2026, Microsoft introduced Majorana 2—a new generation of topological quantum chip. According to the company, the average qubit lifespan has reached 20 seconds, with some instances lasting up to a minute.
The corporation also announced operational speeds of around 1 microsecond, a qubit size of approximately 0.01 mm, and a goal to create a scalable quantum computer by 2029. The company attributed its progress to replacing aluminum with lead in the superconducting layer and utilizing Microsoft Discovery’s AI tools.
Legg’s comments do not directly critique Majorana 2. They pertain to the 2025 article about InAs–Al devices related to Majorana 1. However, Decrypt noted that the dispute touches on the technological foundation upon which Microsoft’s new roadmap is built.
Physicist Sergey Frolov from the University of Pittsburgh told Scientific American that Microsoft’s work in Nature should likely be retracted.
As a reminder, in June, D-Wave Quantum unveiled a roadmap for the phased development of quantum systems, aiming to create a fault-tolerant quantum computer with 100 logical qubits by 2032.