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 $\mathrm{Al}/\mathrm{InAs}$ Josephson junctions in a loop geometry, we measure a $\pi$ jump in the junction phase with an increasing in-plane magnetic field ${\mathit{B}}_{\parallel }$. This jump is accompanied by a minimum of the critical current, indicating a closing and reopening of the superconducting gap, strongly anisotropic in ${\mathit{B}}_{\parallel }$. Our theory confirms that these signatures of a topological transition are compatible with the emergence of Majorana bound states.

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约瑟夫森结的拓扑转换的相位签名

拓扑超导性为容错量子计算提供了希望。虽然平面约瑟夫森结是实现此奇异状态的有吸引力的候选对象，但缺少作为拓扑转换指纹的直接相位测量。通过嵌入两个门可调$铝/\mathrm{铟砷}$ 在回路几何中的约瑟夫森结，我们测量 $\pi$ 随着平面内磁场的增加，跃迁进入结相 ${\mathit{乙}}_{\parallel }$。这种跳跃伴随着最小的临界电流，表明超导间隙的闭合和重新打开，在${\mathit{乙}}_{\parallel }$。我们的理论证实，拓扑转换的这些特征与Majorana约束状态的出现是兼容的。