Researcher challenges Microsoft’s Majorana 2 qubit claim

Henry Legg, a physicist at the University of St Andrews, published a commentary in Nature arguing that Microsoft has not demonstrated a topological qubit on its Majorana 2 chip. Legg directly challenges a 2025 paper by Microsoft Quantum researchers and wrote: “In short: Microsoft haven’t demonstrated the basic physics needed for even a single topological qubit.”

Legg’s critique focuses on experimental procedures and data interpretation. He identifies what he describes as flawed tune‑up routines, software errors in analysis code and the omission of some transport measurements from the public record. He argues that the signals Microsoft attributes to a topological superconducting state could instead arise from experimental noise or from conventional electronic effects such as quantum dots. Legg also notes that the unpublished transport datasets do not clearly show the superconducting gap required to support the claimed state.

Microsoft introduced the Majorana 2 chip earlier this year and reported that it is about 1,000 times more reliable than its predecessor. The company said quantum information on some qubits remained stable for an average of 20 seconds, with individual qubits persisting up to a minute, and that artificial intelligence assisted development by identifying materials, automating tests and improving manufacturing.

In a formal reply published in Nature, Microsoft defended its interpretation and reiterated confidence in the results and its roadmap. Chetan Nayak, Microsoft’s technical fellow and corporate vice president for quantum hardware, wrote that the company “stands by our results and our roadmap.” Microsoft added that the stable signals seen in its experiments are consistent with a topological state and would be unlikely if the system were only noisy or gapless. The company also referenced progress in a DARPA benchmarking program that included independent evaluation of both public and proprietary data.

Topological qubits are a proposed design to store quantum information in ways that are less sensitive to local disturbances. The approach depends on special superconducting states and on the presence of Majorana zero modes; detecting those states typically requires detailed transport measurements and tight control of device conditions. Researchers note that more common electronic states can produce signatures that resemble those expected from a topological superconductor, which makes experimental claims contentious without reproducible evidence.

Both Legg and Microsoft have called for further experiments and independent replication. The dispute has implications for timelines in quantum hardware development and for planning around the point at which quantum computers could affect widely used public‑key cryptography. Scientists in the field say open data and more testing will be needed to resolve the disagreement.