In a superconductor, where electrons move in pairs without resistance, special waves can run along the edges, like ripples along the edge of a carpet. The number of such waves is an important characteristic of the material, but measuring it directly is difficult. Scientists have proposed a clever tool: a movable wall inside the superconductor that separates regions with different "twist" of electron pairs.

When the wall is opened, it becomes a channel for heat. By measuring the amount of heat passing through, you can precisely count how many edge waves run along it. It's like counting people passing through a turnstile by the number of steps. When the wall is closed, it turns into a resonator — a cavity where thermal waves reflect off the walls. If quantum vortices (tiny magnetic knots) are trapped inside, the resonator shifts by half a step. This shift reveals the parity of the number of vortices — whether it's even or odd.

The authors calculated in detail how heat passes through the wall and found a way to distinguish a genuine signal from a false one. A false signal can come from a vortex stuck to the wall from the outside. But by varying temperature, geometry, and monitoring noise, the false vortex gives itself away. Calculations for layers of graphene with a special twist show that loops smaller than a micron at temperatures of thousandths of a kelvin already produce a clear signal. This is a real path to testing exotic superconductors that could become the basis for quantum computers.