A gas junction In superconductors, electrons form a macroscopic wave function that has a definite phase. If two superconductors with different wave function phases are placed in contact with each other through an insulating link, a current will flow through this so-called Josephson's junction without any external voltage. Luick et al. and Kwon et al. observed an analogous phenomenon in a setup that involved two reservoirs of superfluid Fermi gases. Both groups measured the so-called current-phase relation: the dependence of the magnitude of the current on the relative phase. By tuning an external magnetic field, they were able to study how the interactions between fermions affected the nature of the superfluid state. Science, this issue p. 89, p. 84 A Josephson junction was created between two Fermi gas superfluids. The role of reduced dimensionality in high-temperature superconductors is still under debate. Recently, ultracold atoms have emerged as an ideal model system to study such strongly correlated two-dimensional (2D) systems. Here, we report on the realization of a Josephson junction in an ultracold 2D Fermi gas. We measure the frequency of Josephson oscillations as a function of the phase difference across the junction and find excellent agreement with the sinusoidal current phase relation of an ideal Josephson junction. Furthermore, we determine the critical current of our junction in the crossover from tightly bound molecules to weakly bound Cooper pairs. Our measurements clearly demonstrate phase coherence and provide strong evidence for superfluidity in a strongly interacting 2D Fermi gas.

中文翻译：

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超冷二维费米气体中的理想约瑟夫森结

气体结 在超导体中，电子形成具有确定相位的宏观波函数。如果两个具有不同波函数相位的超导体通过绝缘连接相互接触，电流将流过这个所谓的约瑟夫森结，而没有任何外部电压。卢克等人。和权等人。在涉及两个超流体费米气体库的设置中观察到类似的现象。两组都测量了所谓的电流-相位关系：电流幅度对相对相位的依赖性。通过调整外部磁场，他们能够研究费米子之间的相互作用如何影响超流体状态的性质。科学，这个问题 p。89，第。84 在两种费米气体超流体之间形成了约瑟夫森结。降低维数在高温超导体中的作用仍在争论中。最近，超冷原子已成为研究这种强相关二维 (2D) 系统的理想模型系统。在这里，我们报告了在超冷二维费米气体中约瑟夫森结的实现。我们测量约瑟夫森振荡的频率作为结上相位差的函数，并发现与理想约瑟夫森结的正弦电流相位关系非常吻合。此外，我们确定了从紧密结合的分子到弱结合的 Cooper 对交叉中我们结的临界电流。我们的测量清楚地证明了相位相干性，并为强相互作用的二维费米气体中的超流动性提供了强有力的证据。