Assessing the Sensitivity of Niobium- and Tantalum-Based Superconducting Qubits to Infrared Radiation

TL;DR

This study compares niobium and tantalum superconducting qubits, revealing that infrared radiation significantly affects tantalum qubits' coherence, and highlights the importance of filtering and setup design for improving qubit performance.

Contribution

It provides the first direct comparison of infrared sensitivity between niobium and tantalum-based qubits, emphasizing the role of radiative backgrounds in qubit decoherence.

Findings

Infrared radiation channels significantly impact tantalum qubits' decoherence.

Infrared filters reduce tunneling rates to 100 Hz (niobium) and 300 Hz (tantalum).

Tunneling rates exhibit day-scale time dependence, indicating thermal effects.

Abstract

The use of tantalum films for superconducting qubits has recently extended qubit coherence times significantly, primarily due to reduced dielectric losses at the metal-air interface. However, the choice of base material also influences the sensitivity to quasiparticle-induced decoherence. In this study, we investigate quasiparticle tunneling rates in niobium and tantalum-based offset-charge-sensitive qubits. Using a source of thermal radiation, we characterize the sensitivity of either material to infrared radiation and explore the impact of the infrared background through the targeted use of in-line filters in the wiring and ambient infrared absorbers. We identify both radiation channels as significant contributions to decoherence for tantalum but not for niobium qubits and achieve tunneling rates of 100 Hz and 300 Hz for niobium and tantalum respectively upon installation of infrared filters. Additionally, we find a time-dependence in the observed tunneling rates on the scale of days, which we interpret as evidence of slowly cooling, thermally radiating components in the experimental setup. Our findings indicate that continued improvements in coherence times may require renewed attention to radiative backgrounds and experimental setup design, especially when introducing new material platforms.