Impact of Interfacial Atomic Ratios on Stabilized Transport Properties in Defective Josephson Junctions

Defects at the interfaces in the Josephson junction (JJ) are well known as a primary source of decoherence in superconducting quantum devices, indicating the necessity of elucidating defect reaction mechanisms to improve qubit performance. However, their micromechanism remains elusive. Here, we reveal the micromechanism of defects affecting the transport properties by building interfacial defective JJ device models combined with density functional theory (DFT) and nonequilibrium Green's function (NEGF) approach. By comparing the conductance values of various interface classification models with oxygen vacancies (OVs), we find that the aluminum-rich (Al-rich) interface exhibits the smallest conductance variation, resulting in less qubit frequency fluctuations, and this can be further explained by changes in the electrostatic potential relative to the average barrier height. More importantly, the Al-rich interface demonstrates the highest stability. This work provides a theoretical basis and optimization direction for superconducting quantum chip fabrication.