Boffin claims Microsoft's supposed quantum leap does not compute due to 'basic Python errors'

Prestigious journal Nature has published a peer-reviewed critique of Microsoft's claims to have made quantum computing breakthroughs – and the scientist who wrote the paper has essentially said Redmond got it wrong.

Microsoft made its claims of a quantum breakthrough in February 2025 when it revealed tech called Majorana and predicted "this breakthrough will allow us to create a truly meaningful quantum computer not in decades, as some have predicted, but in years."

The software giant's approach to quantum computing involves Majorana particles, subatomic particles that scientists have not observed directly. The company has pursued this approach for years, but experienced reversals that led to the retraction of some papers. Last year, however, Microsoft claimed it had both observed Majorana particles and harnessed them in a quantum computer.

Criticism of that claim was swift and sharp: we reported boffins willing to go on the record as describing Microsoft's work as "unreliable" and perhaps even "fraudulent."

Microsoft insisted its work is sound and in early June 2026 announced Majorana 2, a "next-generation topological quantum chip" it developed with the help of its own agentic AI.

The Windows giant revealed that work after being given a right to reply to a critique of its 2025 Majorana announcement by Dr Henry Legg, a lecturer at the University of St Andrews. Nature accepted Legg's paper on April 20 and scheduled it for publication on June 24.

Titled "On the robustness of topological gap detection via transport," Legg's analysis suggests Microsoft got it wrong.

"Last year they claimed to be years, not decades from a 'topological quantum supercomputer,'" Legg told The Register in an email. "My feeling is that they are centuries, not decades away. If it works at all – and, based on what I have seen, the most likely scenario is that it doesn't work."

Based on his analysis of the research Microsoft published in 2025, Legg argues that the company's claims about finding and being able to control the elusive Majorana particle to build a topological superconductor do not withstand scrutiny.

"I demonstrate that Microsoft's tune-up software is flawed and that coding errors resulted in incorrect statements to peer reviewers," said Legg. "Raw data, which was omitted from the original paper, also appears to indicate Microsoft's devices contain considerable disorder and are not compatible with the existence of a topological gap. In other words, the prerequisites for Microsoft's claims do not appear to be met, but this was obscured because this data did not appear in the original publication."

Essentially, Microsoft has proposed a Topological Gap Protocol (TGP) that can be used to detect the phase transition deemed to be a prerequisite for conducting quantum calculations using Majorana particles.

Legg argues that based on his analysis of underlying transport data (measurements of particle change) – omitted from the original publication – Microsoft chose to focus on results that supported its thesis and ignored data that could be interpreted as a negative result.

As he notes in his critique: "The TGP plotting code was set to highlight only the largest purportedly topological region."

"The primary consequence was the omission of other regions that passed their tune-up protocol (the TGP)," said Legg. "When peer reviewers asked if other regions existed, Microsoft inaccurately stated that they had investigated the only region passing the protocol within the explored range. This was not correct."

Legg also argues that Microsoft mishandled its code. "The code antisymmetrized bias voltage based on array index rather than physical value," his analysis says.

In other words, Microsoft's researchers made a basic programming mistake by evaluating the array index – the number identifying a value's position in an array – instead of the value to which the index refers.

"There were two pretty basic Python programming errors that hid these alternative regions," Legg explained. "Their plotting software was hardcoded with a filter (zbp_cluster_numbers=[1]) that forced it to display only the single largest region, concealing other successful results from their phase maps. Changing this to zbp_cluster_numbers=[1,2] shows already a second region."

Legg added: "The TGP software transformed the data by simply reversing a Python array (x[::-1]) based on its index position, ignoring the actual physical bias voltages."

In a statement provided to The Register, Dr Chetan Nayak, technical fellow and corporate vice president of Microsoft's quantum hardware group, said: "We stand by our results and our roadmap."

"At the end of the day, success is the delivery of a scalable quantum computer. We are confident in our ability to execute against our roadmap and proud of our continued engagement with DARPA, which moved Microsoft into the final phase of its Quantum Benchmarking Initiative after independently evaluating our results – those in the public realm and proprietary – with a team of highly qualified experts. Skepticism and rigor are hallmarks of the scientific process, which we appreciate and have supported from various academics. We have participated in dialogue and our thorough rebuttal was accepted and published by Nature."

Microsoft's rebuttal disputes the validity of Legg's analysis. The software colossus argues its signal measurements were not intended to be exhaustive and that the "minor off-by-one-pixel bug in our TGP processing" is inconsequential.

The response concludes: "In summary, Legg centers on a selective examination of transport tune-up procedures and narrow interpretations of isolated phrases in our referee correspondence, rather than the physical mechanisms underlying the experiment. It relies on unsubstantiated claims about our transport spectra while not engaging with the capacitance measurements at the core of our study, and its alternative treatment of the transport data is inconsistent with more rigorous analyses of the same datasets. Critically, Legg offers no alternative physical model capable of reproducing the capacitance signal or the RTS phenomenology, and does not constitute a substantial scientific challenge to our findings."

Legg thinks that criticism is unfounded.

"They attempt to dismiss these issues as minor bugs, and retrospectively adjust their evidence hierarchy," he said. "In short, Microsoft's reply essentially argues that because they observed a specific capacitance measurement, the prerequisites to do so must have been met. I hope, despite the complexity of the topic, their circular reasoning is clear."

The announcement of Majorana 2 has not changed Legg's assessment of Microsoft's work.

"Majorana 2 is not available to customers and it is not proven to even be a single qubit," Legg said. "Their preprint, which should not really be given any credence given that it is based on a single device, does not even claim an X-measurement (which they did eventually for Majorana 1 last year, but that preprint has also not yet been published). Essentially, their claim of '1,000 times more reliable' refers to the lifetime of a classical bit (the parity of the state). There is no evidence this is a qubit and can hold a superposition. The classical bits in my computer have very long lifetimes (years!), but it does not make them good qubits."

"For Majorana 2, one has to ask why they do not report the X-measurement, since Microsoft were obviously aware it was so important for their claims last year. I think it's very reasonable to assume that they did attempt the same supposed X-measurement with their Majorana 2 device and it didn't work out. That's not surprising because, based on everything I have seen, it all looks like disorder physics and they have not shown any kind of control over even a single qubit." ®