Probing Oxidation-Driven Amorphized Surfaces in a Ta(110) Film for Superconducting Qubit

Journal Article · 26 December 2023 · ACS Nano

DOI: https://doi.org/10.1021/acsnano.3c10740 · OSTI ID:2375788

Mun, Junsik  ^[1]; Sushko, Peter V.  ^[2]; Brass, Emma ^[1]; Zhou, Chenyu  ^[1]; Kisslinger, Kim ^[1]; Qu, Xiaohui ^[1]; Liu, Mingzhao  ^[1]; Zhu, Yimei  ^[3]

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1. Brookhaven National Laboratory (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)
2. Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
3. Brookhaven National Laboratory (BNL), Upton, NY (United States)

Recent advances in superconducting qubit technology have led to significant progress in quantum computing, but the challenge of achieving a long coherence time remains. Despite the excellent lifetime performance that tantalum (Ta) based qubits have demonstrated to date, the majority of superconducting qubit systems, including Ta-based qubits, are generally believed to have uncontrolled surface oxidation as the primary source of the two-level system loss in two-dimensional transmon qubits. Therefore, atomic-scale insight into the surface oxidation process is needed to make progress toward a practical quantum processor. Here, in this study, the surface oxidation mechanism of native Ta films and its potential impact on the lifetime of superconducting qubits were investigated using advanced scanning transmission electron microscopy (STEM) techniques combined with density functional theory calculations. The results suggest an atomistic model of the oxidized Ta(110) surface, showing that oxygen atoms tend to penetrate the Ta surface and accumulate between the two outermost Ta atomic planes; oxygen accumulation at the level exceeding a 1:1 O/Ta ratio drives disordering and, eventually, the formation of an amorphous Ta₂O₅ phase. In addition, we discuss how the formation of a noninsulating ordered TaO_1–δ (δ < 0.1) suboxide layer could further contribute to the losses of superconducting qubits. Subsurface oxidation leads to charge redistribution and electric polarization, potentially causing quasiparticle loss and decreased current-carrying capacity, thus affecting superconducting qubit coherence. The findings enhance the comprehension of the realistic factors that might influence the performance of superconducting qubits, thus providing valuable guidance for the development of future quantum computing hardware.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
• Grant/Contract Number: AC05-76RL01830; SC0012704; AC02−05CH11231; AC05−76RL01830
• OSTI ID: 2375788
• Alternate ID(s): OSTI ID: 2281335
• Report Number(s): PNNL-SA-186621; BNL-225171-2024-JAAM
• Journal Information: ACS Nano, Vol. 18, Issue 1; ISSN 1936-0851
• Publisher: American Chemical Society (ACS)Copyright Statement
• Country of Publication: United States
• Language: English