Confirmation of Spatiotemporally-correlated Qubit Errors from Cosmic Rays*

Quantum computation at scale requires sufficiently infrequent and sparse errors in time and space. In superconducting qubit processors, moments of spatiotemporally-correlated errors are believed to result from ionizing radiation interacting with the device. Here, we demonstrate unambiguous detection of qubit relaxation from cosmic rays, enabled by concurrent monitoring of qubit errors with scintillating radiation detectors and by adopting coincidence-timing techniques from nuclear and high energy physics. We identify the correlation length and duration of spatiotemporally-correlated qubit relaxation events from cosmic rays and estimate the occurrence rate of these events. While most events are from non-cosmogenic sources, such as ionizing radiation from the laboratory environment, we observe that our device is sensitive to nearly all cosmic ray impacts, which marks a possible challenge to future implementations of quantum error correction. These observations underscore a necessity to create quantum devices that are insensitive to all sources of ionizing radiation and highlights a benefit of operating superconducting qubit arrays in a low-background radiation environment.