Probing the TLS Density of States in SiO Films using Superconducting Lumped Element Resonators

TL;DR

This study investigates dielectric losses in amorphous SiO films at cryogenic temperatures using superconducting resonators, revealing an energy-dependent TLS density of states that impacts qubit decoherence.

Contribution

Developed a broadband measurement setup with multiplexed resonators to probe TLS density of states in SiO films at low temperatures and powers.

Findings

TLS density of states is energy dependent.

Dielectric losses match atomic two-level tunneling system predictions.

Reducing qubit frequency may minimize TLS-related decoherence.

Abstract

We have investigated dielectric losses in amorphous SiO thin films under operating conditions of superconducting qubits (mK temperatures and low microwave powers). For this purpose, we have developed a broadband measurement setup employing multiplexed lumped element resonators using a broadband power combiner and a low-noise amplifier. The measured temperature and power dependences of the dielectric losses are in good agreement with those predicted for atomic two-level tunneling systems (TLS). By measuring the losses at different frequencies, we found that the TLS density of states is energy dependent. This had not been seen previously in loss measurements. These results contribute to a better understanding of decoherence effects in superconducting qubits and suggest a possibility to minimize TLS-related decoherence by reducing the qubit operation frequency.