Surface participation and dielectric loss in superconducting qubits

TL;DR

This study investigates how dielectric surface participation affects energy relaxation times in superconducting transmon qubits, revealing that material interfaces are a primary source of dissipation limiting qubit coherence.

Contribution

It introduces a combined simulation and experimental approach to quantify surface participation ratios and links them directly to qubit relaxation times, highlighting dielectric dissipation as a key factor.

Findings

Relaxation rates are approximately proportional to surface participation ratios.

Dielectric dissipation at material interfaces is the main limiting factor for T1.

Surface dielectric dissipation exhibits spatial discreteness.

Abstract

We study the energy relaxation times ($T_1$) of superconducting transmon qubits in 3D cavities as a function of dielectric participation ratios of material surfaces. This surface participation ratio, representing the fraction of electric field energy stored in a dissipative surface layer, is computed by a two-step finite-element simulation and experimentally varied by qubit geometry. With a clean electromagnetic environment and suppressed non-equilibrium quasiparticle density, we find an approximately proportional relation between the transmon relaxation rates and surface participation ratios. These results suggest dielectric dissipation arising from material interfaces is the major limiting factor for the $T_1$ of transmons in 3D cQED architecture. Our analysis also supports the notion of spatial discreteness of surface dielectric dissipation.