# Phase signature of topological transition in Josephson Junctions

## TL;DR

This paper demonstrates phase signatures of topological transitions in Josephson junctions, showing a magnetic-field-induced phase jump and gap closing, consistent with Majorana states, advancing understanding of topological superconductivity.

## Contribution

It provides direct phase measurements as evidence of topological transition in Josephson junctions, a key step in realizing topological quantum computing.

## Key findings

- Observation of a $$-jump in junction phase with magnetic field.
- Critical current minimum indicating gap closing.
- Anisotropic behavior consistent with topological transition theory.

## Abstract

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 ${\bf B}_\|$. Our theory confirms that these signatures of a topological transition are compatible with the emergence of Majorana states.