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

TL;DR

This paper critically examines the topological gap protocol used in a recent study, revealing inconsistencies and unreliable claims about topological superconductivity in InAs-Al devices, and calls for revisiting those conclusions.

Contribution

It identifies fundamental issues in the TGP, showing that its application depends on arbitrary data choices and lacks a consistent definition, challenging prior claims of topological phases.

Findings

TGP lacks a clear, consistent definition of 'gap' and 'topological'

Results depend heavily on data parameters and measurement choices

Claims of high probability of topological phase are unreliable

Abstract

The topological gap protocol (TGP) is presented as "a series of stringent experimental tests" for the presence of topological superconductivity and associated Majorana bound states. Here, we show that the TGP, 'passed' by Microsoft Quantum [PRB 107, 245423 (2023)], lacks a consistent definition of 'gap' or 'topological', and even utilises different parameters when applied to theoretical simulations compared to experimental data. Furthermore, the TGP's outcome is sensitive to the choice of magnetic field range, bias voltage range, data resolution, and number of cutter voltage pairs - data parameters that, in PRB 107, 245423 (2023), vary significantly, even for measurements of the same device. As a result, the core claims of PRB 107, 245423 (2023) are primarily based on unexplained measurement choices and inconsistent definitions, rather than on intrinsic properties of the studied devices. As such, Microsoft Quantum's claim in PRB 107, 245423 (2023) that their devices have a "high probability of being in the topological phase" is not reliable and must be revisited. Our findings also suggest that subsequent studies, e.g. Nature 638, 651-655 (2025), that are based on tuning up devices via the TGP are built on a flawed protocol and should also be revisited.