Can we build a topological qubit in 2025?

I will discuss recent developments in the topological superconducting devices, in particular in relation to the recent claims of Microsoft Quantum. First, I will discuss nonlocal conductance as a purported measure of topological superconductivity [1,2]. In relation to this, I will critically examine the so-called topological gap protocol (TGP). I will demonstrate that the TGP is not a reliable diagnostic tool for the presence of topological superconductivity and associated Majorana Zero Modes [3]. Moreover, I will show that this protocol is also an unreliable method to detect a superconducting gap, a prerequisite for readout of a well-defined parity in a superconductor and the proposed basis of a putative topological qubit [4]. I will discuss this in relation to the recent controversial claims by Microsoft Quantum to have built a topological qubit [5,6].

References:
[1] Hess, Legg, Loss, Klinovaja Phys. Rev. Lett. 130, 207001 (2023)
[2] Feng, Legg, et al. Nat. Phys. (2025)
[3] Legg, arXiv:2502.19560
[4] Legg, arXiv:2503.08944
[5] https://www.nature.com/articles/d41586-025-00683-2
[6] https://www.nature.com/articles/d41586-025-00829-2