Abstract
Improving the qubit’s lifetime (T1) is crucial for fault-tolerant quantum computing. Recent advancements have shown that replacing niobium (Nb) with tantalum (Ta) as the base metal significantly increases T1, likely due to a less lossy native surface oxide. However, understanding the formation mechanism and nature of both surface oxides is still limited. Using aberration-corrected transmission electron microscopy and electron energy loss spectroscopy, we found that Ta surface oxide has fewer suboxides than Nb oxide. We observed an abrupt oxidation state transition from Ta2O5 to Ta, as opposed to the gradual shift from Nb2O5, NbO2, and NbO to Nb, consistent with thermodynamic modeling. Additionally, amorphous Ta2O5 exhibits a closer-to-crystalline bonding nature than Nb2O5, potentially hindering H atomic diffusion toward the oxide/metal interface. Finally, we propose a loss mechanism arising from the transition between two states within the distorted octahedron in an amorphous structure, potentially causing two-level system loss. Our findings offer a deeper understanding of the differences between native amorphous Ta and Nb oxides, providing valuable insights for advancing superconducting qubits through surface oxide engineering.
Original language | English (US) |
---|---|
Journal | ACS nano |
DOIs | |
State | Accepted/In press - 2024 |
Funding
This work was supported by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Superconducting Quantum Materials and Systems Center (SQMS) under contract No. DE-AC02-07CH11359. All electron microscopy and related work were performed using instruments in the Sensitive Instrument Facility at Ames National Lab. The Ames National Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358. R.Z. and B.-C.Z. acknowledge Research Computing at the University of Virginia for providing computational resources and technical support that have contributed to the results reported within this manuscript. URL: https://re.virginia.edu . The authors also thank Rigetti Computing for fabricating the devices used in this study. This work was produced by Iowa State University under Contract DE-AC02CH11358 with the U.S. Department of Energy. Publisher acknowledges the U.S. Government license and the provision to provide public access under the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). Acknowledgments
Keywords
- CALPHAD
- STEM-EELS
- niobium oxides
- superconducting qubits
- surface encapsulation
- tantalum oxides
ASJC Scopus subject areas
- General Materials Science
- General Engineering
- General Physics and Astronomy