Old doubts linger, yet new Microsoft quantum chip raises the stakes

In February, the Microsoft Quantum research group announced a new kind of computer processor called Majorana 1. According to the tech giant, the processor contained the world’s first topological qubits, built with a new material it called a ‘topoconductor’. Majorana 1 contained eight qubits, with Microsoft Quantum saying it would in future hold a million.

The group published its paper in Nature the same day, and that stoked the early concerns about what Microsoft Quantum had actually demonstrated.

Foremost, the paper was considerably more circumspect than Microsoft’s press release. The researchers had built devices made of indium-arsenide-aluminium and discussed a way to measure, in a ‘single shot’, the parity of an electronic state, i.e. whether the number of electrons was odd or even in the state, in the wire.

The team called this measurement a “necessary ingredient” for a highly sought after form of quantum computing.

However, there was a significant gap between the scopes of the paper and of the press release, prompting concerns in the scientific community that Microsoft was trying to lay claim to a commercially lucrative technology without first proving that it actually worked.

Zero modes

Quantum computing is a new, more powerful form of computing that scientists believe can solve some problems much better than conventional devices can. However, the quantum bits, or qubits, these machines are based on are notoriously fragile.

A qubit stores information in a quantum state, which can be disturbed by even the slightest interactions with stray heat or stray magnetic fields. Another technology called quantum error correction can compensate but not without imposing additional technological hurdles.

Many leading quantum computers encode qubits in superconducting circuits, while others use atoms, ions or light. At least on paper, topological quantum computing shows another way.

In this domain, Microsoft Quantum has been trying to build a quantum computer with qubits based on particles called Majorana zero modes (MZMs). Technically, MZMs are ‘emergent quasiparticles’. The physicists Sankar Das Sarma, Roman Lutchyn, and Jay Sau had predicted in 2010 that they would occur at the ends of specially engineered superconducting wires.

Two MZMs separated by some space constitutes a particular quantum state, and whether that state is occupied or not can encode information, like 0 and 1. This way, each MZM pair stores information in both particles together.

This is less like one half being stored in each particle and more like both particles storing the information together: many small disturbances affecting only one end cannot destroy the information, yet both ends are required to access it. The space between the two MZMs of a pair is crucial to achieve this.

MZMs also follow some strange rules. For example, carrying out one exchange of MZMs and then another can create a different quantum state than performing the same exchange in the reverse order.

Airtight inference

But a big problem today is to ascertain if a device with the necessary superconducting wires and other parts also has MZMs. This is because there are many impostor states that are easier to create but which lack the MZMs’ unusual properties. There is no way to directly spot an MZM with some kind of microscope and claim success. Instead, scientists and engineers have to measure the device’s properties in different ways, and from that infer the presence of MZMs.

This inference has to be airtight, and the dispute in the Microsoft case is that its inference is not.

The matter is still on, in fact: on June 2 this year, Microsoft Quantum announced a new processor called Majorana 2 and uploaded a new preprint paper. Here, the team replaced aluminium with lead, whose superconducting state is harder to disrupt, to make the desired state more robust. It also switched to a gallium-antimonide substrate and redesigned the semiconductor stack to reduce disorder.

The upgrade was apparently dramatic: in Microsoft’s telling, the topological gap — the energy needed to excite the system out of its protected state — had increased from around 30 microelectron-volts to 70 microelectron-volts. The parity switching time had also increased from a few milliseconds to around 20 seconds.

The group presented this as proof of topological quantum computing’s promise because the new numbers were indicative of the encoded information being more robustly protected from disturbances. On the back of these reported advances, the company said it would build a scalable quantum computer by 2029 — a significantly shortened deadline considering how complex the technology still is.

Rebuttal and response

However, not everyone is convinced Microsoft learnt the bigger lesson from last time. As University of Pittsburgh professor Sergey Frolov has said, Microsoft’s previous record has left him unwilling to treat the new work as resting on a well-understood foundation.

MZMs are very difficult to create and detect. For example, researchers from TU-Delft in the Netherlands published a paper in Nature in 2018 claiming they had spotted MZMs. But it had to be retracted three years later after independent scientists found problems in the data analysis.

In its 2025 paper, the Microsoft Quantum team used the topological gap protocol it had presented in a 2023 paper: a way to use electrical conductance data to identify combinations of magnetic field and gate voltage that are consistent with gapped MZMs. The team then used a technique called radio-frequency interferometry to check one region of the device, and where the team said the data had evidence of parity switching.

But at an American Physical Society meeting a month later, scientists remained sceptical. The Microsoft team had demonstrated one measurement on one wire in the paper and itself presented additional measurements of a different kind, but many physicists still had doubts.

Cornell University professor Eun-Ah Kim said the data was quite weak while Argonne National Laboratory physicist Kartiek Agarwal called the paper’s claims premature, even if not deserving to be dismissed. Henry Legg, a lecturer at the University of St. Andrews in Scotland, in particular said the headline data came from a small number of measurements on one device.

Then, on June 24 this year, Nature published a rebuttal by Dr. Legg alongside a response from Microsoft Quantum (physicist Chetan Nayak was the corresponding author). In his rebuttal, based on his own work over the last year, Dr. Legg contended that Microsoft’s device itself may not have been qualified to host MZMs, that the underlying data of how electric currents move in the device appeared consistent with a gapless and highly disordered system, and that the topological gap protocol was sensitive, rather than agnostic, to how a researcher chose to analyse the system.

In response, Nayak et al. disputed Dr. Legg’s logic and said its claims were based on the radio-frequency measurements, not the protocol.

Many physicists believe Microsoft’s attempts are promising and commend its transparency with data. But many physicists also remain unconvinced that the qubits in Majorana 1 and Majorana 2 are working topological qubits.