The effects of disorder in superconducting materials on qubit coherence.

Abstract

Introducing disorder in the superconducting materials has been considered promising to enhance the electromagnetic impedance and realize noise-resilient superconducting qubits. Despite a number of pioneering implementations, the understanding of the correlation between the material disorder and the qubit coherence is still developing. Here, we demonstrate a systematic characterization of fluxonium qubits with the superinductors made by spinodal titanium-aluminum-nitride with varied disorder. From qubit noise spectroscopy, the flux noise and the dielectric loss are extracted as a measure of the coherence properties. Our results reveal that the 1/f ^α flux noise dominates the qubit decoherence around the flux-frustration point, strongly correlated with the material disorder; while the dielectric loss are largely similar under a wide range of material properties. From the flux-noise amplitudes, the areal density (σ) of the phenomenological spin defects and material disorder are found to be approximately correlated by <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>σ</mi> <mo>∝</mo> <msubsup><mrow><mi>ρ</mi></mrow> <mrow><mi>x</mi> <mi>x</mi></mrow> <mrow><mn>3</mn></mrow> </msubsup> </math> , or effectively <math xmlns="http://www.w3.org/1998/Math/MathML"> <msup> <mrow><mrow><mo>(</mo> <mrow> <msub><mrow><mi>k</mi></mrow> <mrow><mi>F</mi></mrow> </msub> <mi>l</mi></mrow> <mo>)</mo></mrow> </mrow> <mrow><mo>-</mo> <mn>3</mn></mrow> </msup> </math> . This work has provided new insights on the origin of decoherence channels beyond surface defects and within the superconductors, and could serve as a useful guideline for material design and optimization.