Magnetic bound states embedded in tantalum superconducting thin films

TL;DR

This study reveals that common in situ cleaning methods for tantalum superconducting thin films inadvertently introduce magnetic bound states, which can impair the performance of superconducting qubits by increasing dephasing and energy relaxation.

Contribution

The paper demonstrates that oxygen descumming and argon milling induce magnetic bound states in tantalum films, highlighting a potential source of decoherence in superconducting qubits.

Findings

Cleaning methods introduce magnetic bound states.

Impurities likely cause the bound states.

Bound states affect qubit coherence.

Abstract

In the fabrication of superconducting devices, both in situ and ex situ processes are utilized, making the removal of unwanted oxide layers and impurities under vacuum conditions crucial. Oxygen descumming and argon milling are standard in situ cleaning methods employed for device preparation. We investigated the impact of these techniques on tantalum superconducting thin films using scanning tunneling microscopy at millikelvin temperatures. We demonstrate that these cleaning methods inadvertently introduce magnetic bound states within the superconducting gap of tantalum, likely by oxygen impurities. These bound states can be detrimental to superconducting qubit devices, as they add to dephasing and energy relaxation.