Scientists challenge Microsoft quantum computing 'breakthrough'

Microsoft’s recent claim of creating the first ‘topological qubits’—a major breakthrough in quantum computing—has come under scrutiny, with a physicist questioning the reliability of a key test used to support it. This critique has added to growing skepticism about the company’s announcement, which was made on February 19 without a peer-reviewed paper providing direct evidence of the qubits’ existence. Instead, Microsoft published a study in the Nature journal describing a method for measuring future topological qubits, though it did not confirm their creation.

“While the Nature paper outlined our approach, it does not speak to our progress,” a Microsoft spokesperson stated, adding that significant advancements had occurred since the paper’s submission nearly a year ago. A new article by the Nature journal has published the latest critique from Henry Legg, a physicist at the University of St Andrews in the UK, who has challenged the validity of the topological gap protocol (TGP), a test Microsoft uses to detect Majorana quasiparticles.

Majoranas, which arise from the collective behavior of electrons, are essential for topological qubits. Although Microsoft did not mention the TGP in its February announcement, it later confirmed that the test played a role in their qubit development.

“Since the TGP is flawed, the very foundations of the qubit are not there,” Legg argued in his preprint.

Chetan Nayak, who leads Microsoft’s quantum computing research, dismissed Legg’s critique, saying, “The criticism can be summarized as Legg constructing a false straw man of our paper and then attacking that.”

The Majorana challenge

Majoranas have remained elusive, with previous claims of their discovery often later debunked as false positives. Microsoft researchers introduced the TGP in a 2022 preprint, later published in Physical Review B (PRB), as a method to identify Majoranas with ‘high probability.’ The test relies on electronic measurements from ultracold metal structures, with specific signals indicating the presence of Majoranas.

However, Legg and his colleagues at the University of Basel found that the test could be fooled by ‘doppelgangers’—signals that mimic Majoranas but lack their essential properties. In his latest critique, Legg identified further flaws, including inconsistencies in experimental conditions such as magnetic field strength variations, which could undermine the test’s reliability.

Nayak dismissed this concern, stating, “The ranges come from an initial scan we describe, and we always analyze the full data.”

Legg also pointed out a discrepancy between the TGP’s description in the PRB paper and its implementation in Microsoft’s publicly shared code. While Nayak initially acknowledged the difference in an email, he later reversed course, calling it a “non-issue.”

Carlo Beenakker, a physicist at Leiden University, found Legg’s critique “certainly valid” but remains optimistic about Microsoft’s pursuit of topological qubits. Anton Akhmerov from Delft University believes Microsoft must publicly respond to Legg’s concerns. A Microsoft spokesperson stated they would formally reply if contacted by PRB editors.

Unresolved questions

Some critical details remain undisclosed due to intellectual property concerns, including the code used in Microsoft’s simulations verifying the TGP. While Microsoft has shared some device parameters with Nature, Akhmerov insists that without access to the full source code, the validity of Microsoft’s results cannot be confirmed.

The Nature journal has acknowledged concerns about the protocol but maintains that they do not affect the validity of its paper.

More clarity may come on March 18, when Nayak is scheduled to present Microsoft’s topological qubit data at an American Physical Society meeting. For now, skepticism persists. “There’s no convincing, even mildly convincing, evidence for Majoranas,” Beenakker concluded.

By Nazrin Sadigova