  The Josephson current flowing in a junction between two superconductors is a
striking manifestation of macroscopic quantum coherence, with applications in
metrology and quantum information. This equilibrium current is related with the
formation of Andreev states localized in the junction, whose energy depends
periodically on the superconducting phase difference. Topology emerged as a
guide for predicting exotic properties of Andreev states. In particular,
topological superconductors host Majorana modes at their ends. Then, in a
junction with such leads, the hybridization of two Majorana modes results in an
Andreev state with a period-doubling of its energy-phase dependence.
Furthermore, topologically protected crossings between Andreev states in
junctions with more than two leads may be revealed through a quantized
transconductance. The prediction motivated recent efforts to fabricate
multi-terminal junctions. Here we combine both topological effects to predict a
robust non-vanishing quantized transconductance in trijunctions with
topological leads. Such devices are envisioned to reveal the anyonic nature of
Majorana states through their braiding. Our prediction can be used to assess
that a given junction is indeed suitable to perform its braiding function.
