Gamma-Ray Pair Production in Quantum Device Housing as a Source of Correlated Events

Naturally occurring background radiation including cosmic rays can cause correlated decoherence events in superconducting qubits and disrupt error correction in quantum computers. In this work, cosmic rays at sea level from the cosmic-ray shower generator CRY including muons, pions, protons, neutrons, and gamma rays were propagated through a detailed GEANT4 model of a microwave kinetic inductance detector (MKID). The energy deposition spectrum in the substrate of the MKID following initial gamma rays was found to show prominent features resulting from electron-positron pair production in the MKID housing material. These correlated charged particles from pair production lead to a distinctive class of time-correlated but spatially separated events in quantum devices.