Origin of Mechanical and Dielectric Losses from Two-Level Systems in Amorphous Silicon

Abstract

Amorphous silicon contains tunneling two-level systems, which are the dominant energy loss mechanisms for amorphous solids at low temperatures. These two-level systems affect both mechanical and electromagnetic oscillators and are believed to produce thermal and electromagnetic noise and energy loss. However, it is unclear whether the two-level systems that dominate mechanical and dielectric losses are the same; the former relies on phonon-TLS coupling, with an elastic field coupling constant, $\gamma$, while the latter depends on a TLS dipole moment, $p_0$, which couples to the electromagnetic field. Mechanical and dielectric loss measurements as well as structural characterization were performed on amorphous silicon thin films grown by electron beam deposition with a range of growth parameters. Samples grown at 425 ${}^{\circ }$C show a large reduction of mechanical loss (34 times) and a far smaller reduction of dielectric loss (2.3 times) compared to those grown at room temperature. Additionally, mechanical loss shows lower loss per unit volume for thicker films, while dielectric loss shows lower loss per unit volume for thinner films. Analysis of these results indicate that mechanical loss correlates with atomic density, while dielectric loss correlates with dangling bond density, suggesting a different origin for these two energy dissipation processes in amorphous silicon.

arXiv comment17 pages, 4 figures, 1 table

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• Experimentally revealing anomalously large dipoles in a quantum-circuit dielectric
• Characterization of the low electric field and zero-temperature two-level-system loss in hydrogenated amorphous silicon
• Structural tunability and origin of two-level systems in amorphous silicon
• Characterization of low-loss hydrogenated amorphous silicon films for superconducting resonators
• The strain gap in a system of weakly and strongly interacting two-level systems
• Strategies to reduce the thermoelastic loss of multimaterial coated finite substrates
• Intermodulation spectroscopy and the nonlinear response of two-level systems in superconducting coplanar waveguide resonators
• Connected Network Model for the Mechanical Loss of Amorphous Materials
• Review of Superconducting Qubit Devices and Their Large-Scale Integration