Physicist Challenges Microsoft’s Claims on Topological Qubit

Henry Legg, a physicist at the University of St Andrews, has raised concerns regarding a Microsoft Azure Quantum article published on February 19, 2025, which the tech giant cited to support its assertions about topological qubits. His critique was released on June 24 in the journal Nature.

On the same day, Microsoft responded, contesting Legg’s claims.

Topological qubits are designed to be more error-resistant due to their unique information storage methods.

Details of the Challenge

Legg scrutinized the transport data from Microsoft's 2025 research, which indicates how current flows through an experimental device to ascertain the quantum state of the system. He contends that this data fails to demonstrate a stable superconducting gap in the areas where Microsoft carried out parity readouts. This gap is vital, as its absence complicates the interpretation of the measurements as topological.

He suggests that the signals observed could be attributed to more traditional phenomena, such as quantum dot effects and device disorder, implying that Microsoft may have misidentified non-topological states as indicators of the desired topological regime.

Microsoft's Counterarguments

In response, Microsoft firmly rejected Legg’s conclusions. The company asserted that their measurements do not necessitate an initial assumption of a superconducting gap and that the signals observed align with a topological state. Chetan Nayak, the technical lead for Microsoft Quantum Hardware, emphasized their confidence in their results and future plans.

“We stand by our results and our roadmap,” Nayak stated.

Nayak highlighted Microsoft's participation in a DARPA initiative, which aims to explore the potential for developing a commercially viable quantum computer by 2033, with Microsoft and PsiQuantum selected for a verification phase.

Connection to Majorana 2

On June 2, 2026, Microsoft announced Majorana 2, a next-generation topological quantum chip boasting an average qubit lifespan of 20 seconds, with some lasting up to a minute. The operational speeds are around 1 microsecond, with a qubit size of approximately 0.01 mm, and the goal of creating a scalable quantum computer by 2029. This advancement is credited to innovations such as replacing aluminum with lead in the superconducting layer and employing AI tools from Microsoft Discovery.

While Legg’s critique does not directly address Majorana 2, it pertains to the 2025 article on InAs–Al devices associated with Majorana 1. However, analysts note that the dispute could impact the technological underpinnings of Microsoft’s new initiatives. Sergey Frolov, a physicist at the University of Pittsburgh, suggested that Microsoft's publication in Nature might warrant retraction.

In related news, D-Wave Quantum recently unveiled a phased roadmap aimed at developing a fault-tolerant quantum computer with 100 logical qubits by 2032.