Non-Abelian exchange or fusion of Majorana zero modes
In plain words
The decisive test of Majorana modes is that exchanging or combining them changes a quantum state in a way ordinary particles cannot, and no platform has shown this.
Precise statement
In any Majorana platform, demonstrate the non-Abelian fusion rule (two Majoranas from different pairs fuse to even or odd parity with probability $1/2$ each) or a braiding or measurement sequence implementing the exchange operator $\exp(\pi \gamma_1 \gamma_2 / 4)$, $\gamma_i$ Majorana operators. An answer is measured outcome statistics and gate fidelity that a trivial Andreev-state model cannot reproduce.
What would settle it
A measurement-based braiding protocol with parity readout showing the predicted statistics in a device whose topological phase is independently established.
Status in the literature
Unverified note
Microsoft reported X and Z parity measurements in a tetron device (arXiv:2507.08795, 2025), a prerequisite for measurement-based braiding; no fusion-rule or braiding statistics have been demonstrated as of 2026.