Radon-daughter plate-out source to study radiation effects in qubits

The decay of long-lived, unstable radon daughters that "plate out" on the surfaces of detector materials is known to be problematic in direct detection dark matter experiments. This source of ionizing radiation (alpha particles and heavy ion recoils) has not been studied in the context of superconducitng qubits, where ionizing radiation has been demonstrated to lead to quasiparticle-poisoning-induced decoherence. While the rate of radon plate out in ambient air is quite low and is not currently a dominant source of errors in qubits, as the qubit chips scale up to large arrays, this background may become an important consideration. In order to study this, we have developed an apparatus at the South Dakota School of Mines & Technology (SDSMT) to accelerate and enhance the rate of radon daughter plate out on qubit chips and their enclosures. In this talk, we discuss the apparatus, measurements of plated-out components, the plans for upcoming tests at Fermilab, and provide an outlook for the impact of this background on superconducting qubit chips.