Comment on "InAs-Al hybrid devices passing the topological gap protocol", Microsoft Quantum, Phys. Rev. B 107, 245423 (2023)

Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: Hi, I'm Kai.

Mira: And I'm Mira, here with Lev.

Kai: We're looking at the paper: "Comment on "InAs-Al hybrid devices passing the topological gap protocol", Microsoft Quantum, Phys. Rev. B 107, 245423 (2023)".

Mira: Here's the gist of the paper. The gist The topological gap protocol (TGP) lacks a consistent definition of ‘gap’ or ‘topological’, and even utilises different parameters when applied to theoretical simulations compared to experimental data, meaning the core claims of Microsoft Quantum are unreliable Summary of Issues in PRB 107, 245423 (2023) The comment critically examines the reliability of the topological gap protocol (TGP) as used in Microsoft Quantum's work on InAs-Al hybrid devices, revealing that the protocol is not a stringent or unbiased test for topology.

Kai: The analysis demonstrates that the TGP outcome is highly sensitive to various experimental data parameters, including magnetic field range, bias voltage range, data resolution, and number of cutter voltage pairs.

Mira: These inconsistencies suggest that the reported claims of a "high probability" for the topological phase are primarily based on unexplained measurement choices rather than intrinsic device properties.

Kai: Identification of the ‘gap’ differs between publication and released code The reliability of the TGP hinges on identifying the bulk band gap, and this identification method varies between the published paper and the publicly released code.

Paper summary: Kai: So, we're looking at this paper, "Comment on InAs-Al hybrid devices passing the topological gap protocol," from Microsoft Quantum in Phys Rev B one oh seven twenty four five four two three. Basically, they are saying that the topological gap protocol, or TGP—which they present as these stringent experimental tests for Majorana zero modes—doesn't have a consistent definition of what a ‘gap’ or what ‘topological’ actually means.

Mira: Right. They claim that even when Microsoft Quantum says the TGP 'passed' their devices, there are major inconsistencies in how they are using the protocol and how they define things between their published paper and the code they released. It sounds like a big problem for trusting those initial claims about topological superconductivity.

Lev: From my side, what concerns me is that if you have these measurement parameters changing the outcome so much, it means we can't really say anything intrinsic about the device itself anymore; it’s all tied up in how you set up the experiment.

Kai: Exactly. They point out that this TGP outcome is super sensitive to things like the magnetic field range, the bias voltage range, data resolution, and even which cutter voltage pairs you pick—all these things vary a lot across the measurements of the same device.

Mira: And they show that this sensitivity means those measurement choices are driving the results more than anything else in their study. They argue that it makes it hard to tell if something is actually topological or just an artifact of how you measured it.

Lev: If you're trying to build real hardware, this lack of consistency is a huge headache because you can't rely on a protocol that changes its rules based on your specific experimental setup. You need something robust, not something that depends on fine-tuning every single parameter for every run.

Kai: And they dug deeper into how the definition of the ‘gap’ itself is shaky; in one place, they use a threshold conductance Gth based on high-bias conductance max, but in the released code, it uses the maximum over all bias values instead.

Mira: That difference alone means that what they call a 'gap' by one method is fundamentally different from what they call it by another, and this isn't just a tiny tweak; it changes how you determine the topological phase.

Lev: And that’s where the real issue is for error correction research; if your simulation code uses one definition of gap and your experimental measurement uses another, those two results don't line up at all.

Kai: They also showed that the TGP used for theoretical simulations isn't even the same as what they applied to their actual experimental data, using different analysis routines like analyze two versus analyze two <ref:2502.19560#pg1>.

Mira: That explains why Table two in their paper shows no false positives when using one method, but the TGP used for the figures in the paper does produce false positives, which really undermines their main finding.

Lev: If you're planning to use this protocol to tune your devices, you have to be super careful because you’re essentially tuning based on a flawed measurement standard. That overhead for real hardware runs would be massive if it all depends on these arbitrary choices.

Kai: They also critiqued the definition of 'topological' itself, saying the requirement needs satisfying det(r) less than zero at both ends and for every cutter pair results in only twenty point one percent of phase space being identified as topological under a stronger definition.

Mira: And they added that requiring just one pixel within a region to be ‘topological’ means they are treating mixed trivial and topological regions as the same phase, which inflates how successful the protocol seems overall.

Lev: So, if you're aiming for real quantum hardware, you need a much stricter definition than what they used here because this method lets too much noise in by grouping things together.

Kai: Overall, the whole point of this paper is that the TGP isn't an unbiased test for topology; its results are dictated more by your measurement choices than by any actual property of the device being studied.

Mira: So what does this mean for those who follow this work? It means that claiming a 'high probability' for topological superconductivity in these InAs-Al hybrid devices, as Microsoft Quantum put it in Phys Rev B one oh seven twenty four five four two three, is not reliable at all.

Lev: And that’s a big deal because subsequent studies that try to tune devices up using this TGP are built on a protocol that they just proved is inconsistent and biased. They should definitely be revisited.

Conclusion: Kai: So we've been looking at this Microsoft Quantum paper that comments on their work using what they call the topological gap protocol or TGP for InAs-Al hybrid devices and they're saying it doesn't really pass as a stringent test for topology.

Mira: Right. It's basically saying the definition of 'gap' or 'topological' they used is inconsistent between their published paper and the code they released, which makes their claims about having a high probability of being in that topological phase unreliable.

Lev: From where I sit, that inconsistency is huge because if you try to build real quantum hardware you can’t rely on a protocol where the rules keep changing based on how you set up your measurements.

Kai: Exactly. So the core issue here is that these measurement parameters—like the magnetic field range or bias voltage range—are making the TGP outcome super sensitive, which means they're not testing an intrinsic property of the device at all.

Mira: And they showed that when you look at how they defined 'topological,' it’s pretty weak; requiring just one pixel to be topological lets in mixed trivial and topological regions, which inflates the success of the protocol way too much.

Lev: So what this means for running actual experiments is that any subsequent studies trying to tune devices using this TGP are built on a flawed foundation and they should definitely be revisited.

Kai: It really highlights how critical it is to have a consistent method when you're trying to claim something fundamental about quantum states in these hybrid systems.