Optimization of infrared and magnetic shielding of superconducting TiN and Al coplanar microwave resonators

TL;DR

This study investigates how different shielding methods affect the internal quality factors of superconducting TiN and Al microwave resonators used in quantum circuits, highlighting the effectiveness of combined radiation and magnetic shields.

Contribution

It provides a systematic comparison of shielding effects on TiN and Al resonators, revealing that TiN quality factors are stable while Al resonators benefit from multiple shielding layers.

Findings

TiN resonators maintain high Qi regardless of shielding.

Al resonators show improved Qi with added shielding layers.

Combined radiation and magnetic shields significantly enhance Al resonator performance.

Abstract

We present a systematic study of the effects of shielding on the internal quality factors (Qi) of Al and TiN microwave resonators designed for use in quantum coherent circuits. Measurements were performed in an adiabatic demagnetization refrigerator, where typical magnetic fields of 200 {\mu}T are present at the unshielded sample stage. Radiation shielding consisted of 100 mK and 500 mK Cu cans coated with infrared absorbing epoxy. Magnetic shields consisted of Cryoperm 10 and Sn plating of the Cu cans. A 2.7 K radiation can and coaxial thermalization filters were present in all measurements. TiN samples with Qi = $1.3*10^6$ at 100 mK exhibited no significant variation in quality factor when tested with limited shielding. In contrast, Al resonators showed improved Qi with successive shielding, with the largest gains obtained from the addition of the first radiation and magnetic shields and saturating before the addition of Sn plating infrared absorbing epoxy.