Phase signature of topological transition in Josephson Junctions

Understand

Topological superconductivity holds promise for fault-tolerant quantum computing.

• While planar Josephson junctions are attractive candidates to realize this exotic state, direct phase-measurements as the fingerprint of the topological transition are missing.
• By embedding two gate-tunable Al/InAs Josephson junctions in a loop geometry, we measure a $\pi$-jump in the junction phase with increasing in-plane magnetic field, ${\bf B}_\|$.
• This jump is accompanied by a minimum of the critical current, indicating a closing and reopening of the superconducting gap, strongly anisotropic in ${\bf B}_\|$.