Characterization of two-level system noise for microwave kinetic inductance detector comprising niobium film on silicon substrate

TL;DR

This study demonstrates that increasing the dimensions of niobium-based MKID circuits on silicon substrates effectively suppresses two-level system noise, enhancing detector performance.

Contribution

It confirms for the first time that expanding circuit dimensions reduces TLS noise in niobium MKIDs on silicon substrates.

Findings

Achieved 5.5 dB suppression of TLS noise.

Expanded circuit dimensions from (3 μm, 4 μm) to (5 μm, 23.7 μm).

Validated the effectiveness of geometric modifications for noise reduction.

Abstract

A microwave kinetic inductance detector (MKID) is a cutting-edge superconducting detector. It comprises a resonator circuit constructed with a superconducting film on a dielectric substrate. To expand its field of application, it is important to establish a method to suppress the two-level system (TLS) noise that is caused by the electric fluctuations between the two energy states at the surface of the substrate. The electric field density can be decreased by expanding the strip width (S) and gap width from the ground plane (W) in the MKID circuit, allowing the suppression of TLS noise. However, this effect has not yet been confirmed for MKIDs made with niobium films on silicon substrates. In this study, we demonstrate its effectiveness for such MKIDs. We expanded the dimension of the circuit from (S, W) = (3.00 $\mu$m, 4.00 $\mu$m) to (S, W) = (5.00 $\mu$m, 23.7 $\mu$m), and achieved an increased suppression of 5.5 dB in TLS noise.