Characterization of thermalization timescales in superconducting qubits using quasiparticle poisoning rates*

Quasiparticles, excitations above the superconducting ground state, can lead to errors on superconducting qubits. Various measurements of quasiparticle poisoning of superconducting circuits report slow decays of the poisoning rates following the initial cooling of the low-temperature cryostat. We use weakly charge-sensitive transmons to measure quasiparticle poisoning in qubit arrays. We track these poisoning rates as a function of time after the initial cooldown to characterize the thermalization timescales of our chips. We compare different methods of mounting the devices in our sample boxes, such as adhesive (GE varnish), wire bonds, or machined aluminum clamps.