该研究团队将一个超小的约瑟夫森结嵌入一个高阻抗大约瑟夫森结阵列中，以揭示双重夏皮罗阶跃。对于多个频率，研究人员检测到电路的交流响应与频率为f的微波音调同步，并对应于直流响应中出现的平坦台阶，其电流为2ef，相当于每个微波周期传输一个库珀对。这项工作将相位-电荷对偶性扩展到了约瑟夫森电路，为电路量子电动力学领域提供了广阔的可能性，并且是迈向长期寻求的量子计量电三角封闭的重要一步。
据悉，现代的初级电压标准是基于交流约瑟夫森效应和随之而来的夏皮罗阶跃，其中，应用于约瑟夫森结的微波音调产生的恒定电压hf/2e仅由微波频率f、普朗克常数h和电子电荷e决定。电流和电压的对偶性长期争论表明双重夏皮罗阶跃的可能性——即约瑟夫森结器件可以产生电流阶跃，其高度仅由施加的频率决定。
附：英文原文
Title: Evidence of dual Shapiro steps in a Josephson junction array
Author: Crescini, Nicol, Cailleaux, Samuel, Guichard, Wiebke, Naud, Ccile, Buisson, Olivier, W. Murch, Kater, Roch, Nicolas
Issue&Volume: 2023-03-02
Abstract: The modern primary voltage standard is based on the a.c. Josephson effect and the ensuing Shapiro steps, where a microwave tone applied to a Josephson junction yields a constant voltage hf/2e determined by only the microwave frequency f, Planck’s constant h and the electron charge e. Duality arguments for current and voltage have long suggested the possibility of dual Shapiro steps—that a Josephson junction device could produce current steps with heights determined only by the applied frequency. Here we embed an ultrasmall Josephson junction in a high impedance array of larger junctions to reveal dual Shapiro steps. For multiple frequencies, we detect that the a.c. response of the circuit is synchronized with the microwave tone at frequency f, and the corresponding emergence of flat steps in the d.c. response with current 2ef, equal to the transport of a Cooper pair per tone period. This work extends phase–charge duality to Josephson circuits, which opens a broad range of possibilities in the field of circuit quantum electrodynamics and is an important step towards the long-sought closure of the quantum metrology electrical triangle.
DOI: 10.1038/s41567-023-01961-4
Source: https://www.nature.com/articles/s41567-023-01961-4