Engineering of Niobium Surfaces Through Accelerated Neutral Atom Beam Technology For Quantum Applications

TL;DR

This study introduces a room-temperature Accelerated Neutral Atom Beam (ANAB) technique to precisely engineer niobium surfaces by replacing native oxides with controlled, stable oxides, aiming to enhance qubit coherence in quantum computing.

Contribution

The paper presents a novel application of ANAB technology for controlled surface oxide engineering on niobium, improving surface stability for quantum device performance.

Findings

ANAB can produce Nb-oxide layers 2-6 nm thick.

XPS modeling confirms controlled oxide composition and thickness.

Surface modifications are consistent with TEM and X-ray data.

Abstract

A major roadblock to scalable quantum computing is phase decoherence and energy relaxation caused by qubits interacting with defect-related two-level systems (TLS). 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 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 quality factor. In this work, we present a novel approach to replace the native oxide of niobium (typically formed in an uncontrolled fashion when its pristine surface is exposed to air) with an engineered oxide, using a room-temperature process that leverages Accelerated Neutral Atom Beam (ANAB) technology at 300 mm wafer scale. This ANAB beam is composed of a mixture of argon and oxygen, with tunable energy per atom, which is rastered across the wafer surface. The ANAB-engineered Nb-oxide thickness was found to vary from 2 nm to 6 nm depending on ANAB process parameters. Modeling of variable-energy XPS data confirm thickness and compositional control of the Nb surface oxide by the ANAB process. These results correlate well with those from transmission electron microscopy and X-ray reflectometry. Since ANAB is broadly applicable to material surfaces, the present study indicates its promise for modification of the surfaces of superconducting quantum circuits to achieve longer coherence times.