Experts Weigh in on Microsoft’s Topological Qubit Claim

“The peer-reviewed publication is quite clear [that it contains] no proof for topological qubits,” says Winfried Hensinger, a physicist at the University of Sussex, UK, who works on quantum computing using trapped ions. “But the press release speaks differently. In academia that’s a big no-no: You shouldn’t make claims that are not supported by a peer-reviewed publication”–or that have at least been presented in a preprint.

Chetan Nayak, leader of Microsoft Azure Quantum, which is based in Redmond, Washington, says that the evidence for a topological qubit was obtained in the period between submission of the paper in March 2024 and its publication. He will present those results at a talk at the Global Physics Summit of the American Physical Society in Anaheim, California, in March.

But Hensinger is concerned that “the press release doesn’t make it clear what the paper does and doesn’t contain.” He worries that some might conclude that the strong claim of having made a topological qubit is now supported by a paper in Nature. “We don’t need to make these claims–that is just unhealthy and will really hurt the field,” he says, because it could lead to unrealistic expectations about what quantum computers can do.

As with the qubits used in current quantum computers, such as superconducting components or trapped ions, MZMs would be able to encode superpositions of the two readout states (representing a 1 or 0). By quantum entangling such qubits, information could be manipulated in ways not possible for classical computers, greatly speeding up certain kinds of computation. In MZMs the two states are distinguished by “parity”: whether the quasiparticles contain even or odd numbers of electrons.

As MZMs are “topological” states, their settings cannot easily be flipped by random fluctuations to introduce errors into the calculation. Rather, the states are like a twist in a buckled belt that cannot be smoothed out unless the buckle is undone. Topological qubits would therefore suffer far less from the errors that afflict current quantum computers, and which limit the scale of the computations they can support. Because quantum error correction is one of the most challenging issues for scaling up quantum computers, “we want some built-in level of error protection,” explains Nayak.

It has long been thought that MZMs might be produced at the ends of nanoscale wires made of a superconducting material. Indeed, Microsoft researchers have been trying for several years to fabricate such structures and look for the characteristic signature of MZMs at their tips. But it can be hard to distinguish this signature from those of other electronic states that can form in these structures.

In 2018 researchers at labs in the US and the Netherlands (including the Delft University of Technology and Microsoft), claimed to have evidence of an MZM in such devices. However, they then had to retract the work after others raised problems with the data. “That history is making some experts cautious about the new claim,” says Aaronson.

Now, though, it seems that Nayak and colleagues have cracked the technical challenges. In the Nature paper, they report measurements in a nanowire heterostructure made of superconducting aluminum and semiconducting indium arsenide that are consistent with, but not definitive proof of, MZMs forming at the two ends. The crucial advance is an ability to accurately measure the parity of the electronic states. “The paper shows that we can do these measurements fast and accurately,” says Nayak.

“The device is a remarkable achievement from the materials science and fabrication standpoint,” says Ivar Martin, a materials scientist at Argonne National Laboratory in Illinois. “They have been working hard on these problems, and seems like they are nearing getting the complexities under control.” In the press release, the Microsoft team claims now to have put eight MZM topological qubits on a chip called Majorana 1, which is designed to house a million of them.

Even if the Microsoft claim stands up, a lot will still need to be done to get from a single MZM to a quantum computer, says Hensinger. Topological quantum computing is “probably 20–30 years behind the other platforms,” he says. Martin agrees. “Even if everything checks out and what they have realized are MZMs, cleaning them up to take full advantage of topological protection will still require significant effort,” he says.

Regardless of the debate about the results and how they have been announced, researchers are supportive of the efforts at Microsoft to produce a topological quantum computer. “As a scientist who likes to see things tried, I’m grateful that at least one player stuck with the topological approach even when it ended up being a long, painful slog,” says Aaronson.

“Most governments won’t fund such work, because it’s way too risky and expensive,” adds Hensinger. “So it’s very nice to see that Microsoft is stepping in there.”

Reprinted with permission from Physics World , a publication of the Institute of Physics. Read the original article here.