We report a probable observation of the dc Josephson effect in mesoscopic junctions of three and four superconductors. The devices are fabricated in a top-down fashion from a hybrid semiconductor-superconductor $\mathrm{InAs}/\mathrm{Al}$ epitaxial heterostructure. In general, the critical current of an $N$-terminal junction is an ($N-1$)-dimensional hypersurface in the space of bias currents, which can be reduced to a set of critical current contours. The geometry of critical current contours exhibits nontrivial responses to electrical gating, magnetic field, and phase bias, and it can be reproduced by the scattering formulation of the Josephson effect generalized to the case of $N>2$. Besides establishing solid ground beneath a host of recent theory proposals, our experiment accomplishes an important step toward creating trijunctions of topological superconductors, essential for braiding operations.

中文翻译：

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多端约瑟夫森效应

我们报告了在三个和四个超导体的介观结中的直流约瑟夫森效应的可能观察结果。这些器件由混合半导体超导体以自顶向下的方式制造$\mathrm{铟砷}/铝$外延异质结构。一般而言，$ñ$-终端结点是（$ñ-\mathrm{1个}$）在偏置电流空间中的超曲面，可以将其缩小为一组临界电流轮廓。临界电流轮廓线的几何形状表现出对电门控，磁场和相位偏置的非平凡响应，并且可以通过将约瑟夫森效应的散射公式推广到以下情况来再现它：$ñ>2$。除了在许多最新的理论建议下奠定坚实基础之外，我们的实验还朝着创建拓扑超导体的三结点迈出了重要的一步，这对于编织操作至关重要。