The multi-terminal Josephson effect

Junctions of more than two superconducting terminals are required for implementing braiding operations on Majorana fermions. Moreover, such multi-terminal Josephson Junctions (JJ) were predicted to support topological state and host zero-energy quasiparticles. Unlike conventional two-terminal JJs where the value of critical current is a number, the multi-terminal JJs exhibit a novel feature – the critical current contour (CCC). We report the measurement of non-trivial CCC shapes as a function of gate voltage and magnetic field in hybrid semiconductor/superconductor (InAs/Al) multi-terminal JJs. Multi-terminal junctions can host two different regimes: a strong neighbor-coupling regime and a multi-terminal regime, depending on the gate voltage. The geometry of a junction is also an important factor defining the operating regime. The effect of a perpendicular magnetic field indicates an observation of the Fraunhofer interference pattern in multi-terminal JJs.