Reversing Hydrogen-Related Loss in α-Ta Thin Films for Quantum Device Fabrication

Area of Science:

• Quantum Computing
• Materials Science
• Superconductivity

Background:

• Alpha-tantalum (α-Ta) is a promising material for superconducting qubits due to its low microwave loss native oxide.
• Hydrogen absorption during fabrication can increase microwave loss, degrading qubit performance.

Purpose of the Study:

• To investigate the impact of hydrogen absorption on α-Ta thin films.
• To identify methods for mitigating hydrogen-induced degradation in α-Ta based quantum devices.

Main Methods:

• Exposure of α-Ta thin films to 10 vol% hydrofluoric acid.
• Fabrication and characterization of high-Q resonators at millikelvin temperatures.
• Annealing experiments in ultra-high vacuum (UHV) at 500°C.

Main Results:

• Hydrogen absorption was observed in α-Ta films exposed to hydrofluoric acid for 3 minutes or longer.
• This absorption led to increased power-independent ohmic loss in resonators.
• Annealing at 500°C in UHV for 1 hour fully removed hydrogen and restored intrinsic quality factors to ~4 million.

Conclusions:

• Identified a novel hydrogen-induced loss mechanism in α-Ta superconducting qubits.
• Demonstrated a viable annealing process to reverse hydrogen degradation.
• Findings support robust fabrication of α-Ta and niobium-based quantum devices.