Quantronics Group, Service de Physique de l'État Condensé (CNRS, URA 2464), IRAMIS, CEA-Saclay, 91191 Gif-sur-Yvette, France.
Nature. 2013 Jul 18;499(7458):312-5. doi: 10.1038/nature12315.
The Josephson effect describes the flow of supercurrent in a weak link-such as a tunnel junction, nanowire or molecule-between two superconductors. It is the basis for a variety of circuits and devices, with applications ranging from medicine to quantum information. Experiments using Josephson circuits that behave like artificial atoms are now revolutionizing the way we probe and exploit the laws of quantum physics. Microscopically, the supercurrent is carried by Andreev pair states, which are localized at the weak link. These states come in doublets and have energies inside the superconducting gap. Existing Josephson circuits are based on properties of just the ground state of each doublet, and so far the excited states have not been directly detected. Here we establish their existence through spectroscopic measurements of superconducting atomic contacts. The spectra, which depend on the atomic configuration and on the phase difference between the superconductors, are in complete agreement with theory. Andreev doublets could be exploited to encode information in novel types of superconducting qubits.
约瑟夫森效应描述了在两个超导体之间的弱连接（如隧道结、纳米线或分子）中超流的流动。它是各种电路和设备的基础，应用范围从医学到量子信息。使用类似于人工原子的约瑟夫森电路的实验正在彻底改变我们探测和利用量子物理定律的方式。从微观上看，超流由安德烈夫对态携带，安德烈夫对态定域在弱连接处。这些态是二重态，能量位于超导能隙内。现有的约瑟夫森电路基于每个二重态的基态的性质，到目前为止，尚未直接检测到激发态。在这里，我们通过超导原子接触的光谱测量来证明它们的存在。这些光谱取决于原子的配置和超导体之间的相位差，与理论完全一致。安德烈夫二重态可以被用来在新型超导量子位中编码信息。
