Computed models of natural radiation backgrounds in qubits and superconducting detectors

TL;DR

This paper models natural radiation backgrounds affecting superconducting qubits and detectors using Geant4, providing analytic expressions for radiation-induced decoherence rates based on environmental and material parameters.

Contribution

It introduces a comprehensive modeling approach for natural radiation backgrounds in superconducting electronics, including analytic formulas for key decoherence rates.

Findings

Modeled radiation rates align with experimental measurements.

Rates depend on elevation, material, and geometry.

Provides analytic expressions for radiation effects.

Abstract

Naturally occurring radiation backgrounds cause correlated decoherence events in superconducting qubits. These backgrounds include both gamma rays produced by terrestrial radioisotopes and cosmic rays. We use the particle-transport code Geant4 and the PARMA summary of the cosmic-ray spectrum to model both sources of natural radiation and to study their effects in the typical substrates used in superconducting electronics. We focus especially on three rates that summarize radiation's effect on substrates. We give analytic expressions for these rates, and how they depend upon parameters including laboratory elevation, substrate material, ceiling thickness, and wafer area and thickness. The modeled rates and the distribution of event energies are consistent with our earlier measurement of radiation backgrounds using a silicon thermal kinetic-inductance detector.