Gao Yumei, Shen Yaohong, Chi Feng, Yi Zichuan, Liu Liming
School of Electronic and Information Engineering, UEST of China, Zhongshan Institute, Zhongshan 528400, China.
South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China.
Micromachines (Basel). 2024 Sep 30;15(10):1225. doi: 10.3390/mi15101225.
We study theoretically the Josephson current through a junction composed of quadruple quantum dots (QDs), of which only one is coupled directly to the left and right superconductor leads (denoted by QD1). The other three QDs are side-coupled to QD1 and free from coupling to the leads. It is found that when the energy levels of all the four QDs are identical, the Josephson current varying with energy level of QD1 develops three peaks with two narrow and one wide, showing the typical Dicke lineshape. With increasing inter-dot coupling strength, the triple-peak configuration is well retained and accompanied by an obviously increased current amplitude. The critical current as a function of the energy level of QD1 shows a single resonance peak whose position and height depend on the energy levels of the side-coupled QDs and the inter-dot coupling strengths. We also find that the curve of the critical current versus energy levels of the side-coupled QDs shows a pair of Fano resonances and the same number Fano antiresonances (valleys). When the energy levels of the side-coupled QDs are different from each other, another Fano resonance and antiresonance are induced due to the quantum interference effect. The present results are compared with those in double and triple QDs systems, and may serve as unique means, such as the combination of quantum Dicke and Fano effects, to manipulate the Josehpson currents.
我们从理论上研究了通过由四个量子点（QD）组成的结的约瑟夫森电流，其中只有一个量子点直接与左右超导引线耦合（记为QD1）。其他三个量子点与QD1侧耦合，且不与引线耦合。研究发现，当所有四个量子点的能级相同时，随QD1能级变化的约瑟夫森电流会出现三个峰，其中两个窄峰和一个宽峰，呈现出典型的迪克线形。随着点间耦合强度的增加，三峰结构得到很好的保留，同时电流幅度明显增大。临界电流作为QD1能级的函数呈现出一个单共振峰，其位置和高度取决于侧耦合量子点的能级和点间耦合强度。我们还发现，临界电流与侧耦合量子点能级的曲线呈现出一对法诺共振和相同数量的法诺反共振（谷）。当侧耦合量子点的能级彼此不同时，由于量子干涉效应会诱导出另一个法诺共振和反共振。将目前的结果与双量子点和三量子点系统中的结果进行了比较，这些结果可能作为一种独特的手段，例如量子迪克效应和法诺效应的结合，来操纵约瑟夫森电流。
