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Accepted · first revision · record

Title: Origin of the parity signal in Majorana interferometer devices
Plain: Microsoft reported reading whether a nanowire holds an even or odd number of electrons through a flux-sensitive capacitance signal, and it is disputed whether this signal comes from Majorana modes or ordinary states.
Precise: In the InAs-Al interferometric device of Microsoft Quantum (Nature 638, 651, 2025) and later tetron devices (arXiv:2507.08795), the quantum capacitance shows a bimodal, flux-dependent signal with millisecond-scale switching. Determine whether it reflects the fermion parity of a topological wire with Majorana end modes or trivial Andreev states and quasiparticle poisoning. An answer is an identification supported by measurements that distinguish the two, such as dependence on wire length, field and bulk gap.
Settled by: Measurement of the bulk topological gap in the same device together with the parity-signal dependence on wire length and field across the predicted phase boundary.
Kind: well-posed
Answer type: identification
References: (empty)
Literature status: contested
Status note: The Nature paper states that its data alone do not establish topological modes; a 2025 comment (arXiv:2503.08944) argues the measured regions are gapless; unresolved as of 2026.
Posed since: 2025