Near-Field Localization of the Boson Peak on Tantalum Films for Superconducting Quantum Devices

Abstract

Superconducting circuits are among the most advanced quantum computing technologies; however, their performance is limited by losses found in surface oxides and disordered materials. In this work, we demonstrate the identification and spatial localization of a near-field signature of loss centers on tantalum films using terahertz scattering-type scanning near-field optical microscopy. By utilizing terahertz nanospectroscopy, we observe a localized excess vibrational mode around 0.5 THz and identify this resonance as the boson peak, a signature of amorphous materials. Grazing-incidence wide-angle X-ray scattering reveals that oxides on freshly solvent-cleaned samples are amorphous, whereas crystalline phases emerge after aging in air. Through nanoscale localization of defect centers, our findings provide valuable insights for the optimization of fabrication procedures for new low-loss superconducting circuits.

Probing Oxidation-Driven Amorphized Surfaces in a Ta(110) Film for Superconducting Qubit

“…The Ta metal area beneath the oxidized surface was found to be robust and uniform against oxidation. It is noteworthy that crystallization of the native oxidized Ta amorphous layer by aging effects is not observed in our sample . The Ta atomic lattice is clearly visible at atomic resolution, while the oxidized amorphous layer lacks an ordered atomic arrangement (Figure c).…”

“…It is noteworthy that crystallization of the native oxidized Ta amorphous layer by aging effects is not observed in our sample. 43 The Ta atomic lattice is clearly visible at atomic resolution, while the oxidized amorphous layer lacks an ordered atomic arrangement (Figure 2c). Interestingly, a well-ordered utmost layer of the Ta film in a monatomic thickness is observed at the interface between the crystalline Ta and the amorphous oxide.…”

Structure and Formation Mechanisms in Tantalum and Niobium Oxides in Superconducting Quantum Circuits

“…Niobium (Nb)-based superconducting quantum devices have dominated the field for an extended period as this material offers cost advantages, flexibility in deposition methodologies, and compatibility with industrial-scale processes. , Nonetheless, as the T 1 of two-dimensional transmon qubits composed of Nb has long plateaued around 100 μs, it has become clear that alternative materials approaches are needed . Recent work highlights Nb surface oxides’ critical role in limiting T 1 .…”