Majorana zero modes observed by Microsoft?

[atyy]

https://arxiv.org/abs/2207.02472
InAs-Al Hybrid Devices Passing the Topological Gap Protocol
"We present measurements and simulations of semiconductor-superconductor heterostructure devices that are consistent with the observation of topological superconductivity and Majorana zero modes."

Sergey Frolov and Vincent Mourik review the paper skeptically.

Condensed Matter Theory Center (University of Maryland) reviews the paper as being convincing.

The demonstration of Majoranan zero modes (MZM) would be an important step towards topological quantum computing. Previous claims were shown (in large part due to Frolov and Mourik's efforts) to be incorrect.

 

[gentzen]

Scott Aaronson now also invited discussion about that paper:

(3) The Microsoft team has finally released its promised paper about the detection of Majorana zero modes (“this time for real”), a major step along the way to creating topological qubits. See also this live YouTube peer review—is that a thing now?—by Vincent Mourik and Sergey Frolov, the latter having been instrumental in the retraction of Microsoft’s previous claim along these lines. I’ll leave further discussion to people who actually understand the experiments.

The main points of the only reaction so far are:

a – I have immense respect to Sergey and Vincent who are taking on the Microsoft juggernaut as well as powerful theorists, just by themselves. It seems like anybody who is working on this topic from academia is more or less affiliated with this paper. Makes one wonder: who is going to review this paper impartially? ...

b- While their courage and openness are great, it does feel a little bit unfair to reduce a 40+ page paper that took years of human hours into Twitter sound bites. In peer review, the authors are given a chance to respond to and deliberate with the referees, ...

 

[gentzen]

I have the impression that quantum computing related questions don't receive much attention here. In fact, most such questions might better be asked at QuantumComputing.SE, where many quantum computing experts are present. Even those few quantum computing experts like @Strilanc that post here seem to prefer answering (and asking) such questions over there.

I looked over there to learn more about the general opinion regarding Majorana qubits. The most relevant thing I found was him trying to understand If Majorana qubits are analogous to surface codes, why do the diagrams use lines instead of squares? His later self-answer explains in easy terms how the apparent "conservation of difficulty" violation of Majorana qubits arises, and James Wootton's earlier answer identifies basically the same crucial spot where Majorana qubits will likely break down:

To prevent this, you would need to increase the width of the chain. Once you make this width scale with the code distance, and given that the length must too, you get the quadratic scaling of any surface code approach.

So why do majoranas on nanowires avoid this? Well, perhaps they don't. The single γ_j error event corresponds to quasiparticle poisoning in nanowires. This is a big potential problem, and an ongoing source of research.

So the main difference is that quasiparticle poisoning is a clear fatal problem in surface codes when one tries to make linear codes. The solution is clear in this case: make square codes. For nanowires, quasiparticle poisoning is a more complex issue without a clear solution yet (as far as I know).

This does not directly address the actual question whether the experiments documented in that paper provide conclusive evidence for Majorana zero modes. But it hints at the answer to whether the results of that paper will enable robust topological quantum computing in the distant future.