Correlated Quasiparticle Poisoning from Phonon-Only Events in Superconducting Qubits.

Errors that are correlated across a qubit array pose an obstacle to quantum error correction. We observe elevated correlated poisoning rates in superconducting qubit arrays at the start of a cooldown followed by power-law reductions in time, while the rate of offset charge shifts remains constant, evidence of nonionizing sources of pair-breaking phonon bursts. We also investigate different sample packages, with some exhibiting elevated poisoning due to mechanical impacts from the cryocooler. Possible sources include relaxation of built-up stress in device thin films, substrates, or packaging.