What is it about?

Reducing microwave loss by “surface engineering” can be a key enabler for pushing performance forward with devices of higher intrinsic quality factor. In this work, we have replaced the native oxide of Nb with an engineered oxide, using a process that leverages ANAB technology at 300 mm wafer scale.

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Why is it important?

A major roadblock to scalable quantum computing is phase decoherence and energy relaxation caused by qubits interacting with defect-related two-level systems (TLSs). Native oxides present on the surfaces of superconducting metals used in quantum devices are acknowledged to be a source of TLS that decrease qubit coherence times. Reducing microwave loss by “surface engineering” (i.e., replacing the uncontrolled native oxide of superconducting metals with a thin, stable surface with predictable characteristics) can be a key enabler for pushing performance forward with devices of higher intrinsic quality factor.


In recent years, a major component of microwave loss in state-of-the-art quantum devices has been attributed to native oxides that grow on various materials upon exposure to ambient air. Niobium (Nb) has been widely used in the fabrication of superconducting single-flux quantum circuits, and as the material for interconnects, feedlines, and coplanar waveguide resonators in multi-qubit quantum computing systems. However, many researchers have noted that Nb forms a complex native oxide composed of a mixture of Nb2O5, NbO2, NbO, and other suboxides. Using the ANAB process, we developed an innovative approach to engineer the niobium oxide structures at room temperature to form a stable and engineered (2 to 6 nm thick) Nb-oxide by changing the oxygen fluence. Our initial results from ANAB-treated Nb samples look promising and underscore their potential to be used for fabricating high-Q resonators for quantum applications.

Dr. Soumen Kar

Read the Original

This page is a summary of: Engineering of niobium surfaces through accelerated neutral atom beam technology for quantum applications, Journal of Applied Physics, July 2023, American Institute of Physics,
DOI: 10.1063/5.0153617.
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