Numerical Modeling of Phonon-Mediated Quasiparticle Generation in Superconducting Qubits

Correlated errors in qubit arrays are detrimental to quantum error correction schemes. Recent studies have shown that on-chip impacts of gamma-rays and muons can cause correlated errors in superconducting qubit arrays due to phonon-mediated quasiparticle (QP) poisoning. Understanding the dynamics of phonons in these devices is paramount to developing and improving existing mitigation strategies. In this talk, we present a numerical model of acoustic phonon transport in a Si-crystal using Geant4 for Condensed Matter Physics (G4CMP), a low-temperature Monte-Carlo simulation package. We include both normal metal and superconducting film boundaries, in order to model recent experiments demonstrating a QP poisoning mitigation strategy based on back-side normal metal reservoirs. With this model, we make quantitative predictions of the efficiency of phonon downconversion for different device configurations.