Correlating Superconducting Qubit Performance Losses to Sidewall Near-Field Scattering via Terahertz Nanophotonics

TL;DR

This paper introduces noninvasive terahertz nano-imaging and spectroscopy techniques to diagnose and correlate sidewall scattering and dielectric responses with superconducting qubit coherence, offering a high-throughput method for improving quantum device performance.

Contribution

It demonstrates the use of terahertz near-field methods as a noninvasive, high-throughput diagnostic tool for superconducting qubits, linking material properties to coherence losses.

Findings

THz nano-imaging reveals sidewall near-field scattering correlated with qubit coherence.

THz hyperspectral line scans probe dielectric responses at Al junction interfaces.

Terahertz methods offer a promising proxy for optimizing qubit fabrication processes.

Abstract

Elucidating dielectric losses, structural heterogeneity, and interface imperfections is critical for improving coherence in superconducting qubits. However, most diagnostics rely on destructive electron microscopy or low-throughput millikelvin quantum measurements. Here, we demonstrate noninvasive terahertz (THz) nano-imaging/-spectroscopy of encapsulated niobium transmon qubits, revealing sidewall near-field scattering that correlates with qubit coherence. We further employ a THz hyperspectral line scan to probe dielectric responses and field participation at Al junction interfaces. These findings highlight the promise of THz near-field methods as a high-throughput proxy characterization tool for guiding material selection and optimizing processing protocols to improve qubit and quantum circuit performance.