Fluctuation Spectroscopy of Two-Level Systems in Superconducting Resonators

TL;DR

This paper investigates how two-level systems in amorphous dielectrics affect superconducting resonators, using long-term measurements and simulations to understand loss and noise reduction at different power levels.

Contribution

It introduces a detailed experimental and simulation study of TLS-induced loss and noise in superconducting resonators across various power regimes.

Findings

Loss and noise decrease at medium and high power levels.

Experimental results align with TLS interaction model simulations at higher powers.

Long-term measurements reveal power-dependent decoherence effects.

Abstract

Superconducting quantum computing is experiencing a tremendous growth. Although major milestones have already been achieved, useful quantum-computing applications are hindered by a variety of decoherence phenomena. Decoherence due to two-level systems (TLSs) hosted by amorphous dielectric materials is ubiquitous in planar superconducting devices. We use high-quality quasilumped element resonators as quantum sensors to investigate TLS-induced loss and noise. We perform two-tone experiments with a probe and pump electric field; the pump is applied at different power levels and detunings. We measure and analyze time series of the quality factor and resonance frequency for very long time periods, up to 1000 h. We additionally carry out simulations based on the TLS interacting model in presence of a pump field. We find that loss and noise are reduced at medium and high power, matching the simulations, but not at low power.