A team of researchers, led by scientist Lin Zhou of Ames National Laboratory, has made important progress towards understanding the role of surface oxides in improving quantum computing circuits performance. Surface oxides are a primary cause of decoherence, or loss of quantum properties in quantum circuits. The team is part of a larger effort by the Superconducting Quantum Materials and Systems Center (SQMS) to improve quantum computers.
SQMS center researchers are currently making a full investigation into the origin of decoherence. It can cause errors in quantum information and limit the time in which quantum information can be processed and stored. Decoherence is one of the biggest obstacles to the success of quantum computing technology.
“There is a lack of systemic understanding,” said Zhou. “What if we change one parameter during device fabrication? How will that change the material and the device performance?
Zhou explained that they are using various techniques to analyze material down to the atomic level. With the data collected, they aim to establish connections between specific defects in a device and coherence loss.
“Different types of microscopes help us understand what's happening inside the material from different perspectives, allowing us to diagnose why a material exhibits certain properties,” said Zhou, who mainly uses electron microscopy to investigate material’s structure and chemistry.
“We try to see how atoms are arranged and whether there are suspicious features or defects linked to the device's performance deterioration.”
In one project, Ames Lab scientists worked with researchers from Rigetti Computing, Fermi National Laboratory, and the Illinois Institute of Technology. By using advanced imaging and analysis techniques, they explored the relationship between material microstructures and resulting properties. This approach helped clarify how material structures can result in decoherence.
In another project, Ames Lab scientists compared a niobium-based material with a tantalum-based material. Zhou explained that niobium (Nb) and tantalum (Ta) are good superconductive materials with many similarities. But through their work, they unexpectedly found structural differences between the two that showed devices made with Ta film had better performance.
“It's a bottom-up approach,” said Zhou. “We start by understanding the materials from the atomic level and applying that understanding to influence material growth and performance.”
This research is further discussed in:
“Structure and Formation Mechanisms in Tantalum and Niobium Oxides in Superconducting Quantum Circuits,” written by Jin-Su Oh, Rahim Zaman, Akshay A. Murthy, Mustafa Bal, Francesco Crisa, Shaojiang Zhu, Carlos G. Torres-Castanedo, Cameron J. Kopas, Joshua Y. Mutus, Dapeng Jing, John Zasadzinski, Anna Grassellino, Alex Romanenko, Mark C. Hersam, Michael J. Bedzyk, Matt Kramer, Bi-Cheng Zhou, and Lin Zhou, and published in ACS Nano.
“Exploring the relationship between deposition method, microstructure, and performance of Nb/Si-based superconducting coplanar waveguide resonators,” written Jin-Su Oh, Cameron J. Kopas, Jayss Marshall, Xiaotian Fang, Kamal R. Joshi, Amlan Datta, Sunil Ghimire, Joong-Mok Park, Richard Kim, Daniel Setiawan, Ella Lachman, Joshua Y. Mutus, Akshay A. Murthy, Anna Grassellino, Alex Romanenko, John Zasadzinski, Jigang Wang, Ruslan Prozorov, Kameshwar Yadavalli, Matt Kramer, and Lin Zhou, and published in Acta Materialia.
The Superconducting Quantum Materials and Systems Center is one of the five U.S. Department of Energy National Quantum Information Science Research Centers. Led by Fermi National Accelerator Laboratory, SQMS is a collaboration of more than 30 partner institutions — national labs, academia and industry — working together to bring transformational advances in the field of quantum information science.
Ames National Laboratory is a U.S. Department of Energy Office of Science National Laboratory operated by Iowa State University. Ames Laboratory creates innovative materials, technologies, and energy solutions. We use our expertise, unique capabilities, and interdisciplinary collaborations to solve global problems.
Ames Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit https://energy.gov/science.