Diagnosis and Mitigation of Correlated Errors in Superconducting Qubits from Ionizing Radiation*

Ionizing radiation causes momentary events of spatially-correlated superconducting qubit errors. We present the detection of multi-qubit correlated relaxation events in coincidence with cosmic ray secondary particles using scintillating detectors. These measurements identify the overall proportion of qubit errors caused by cosmic ray secondary particles versus all other sources of relaxation errors. The in-situ detection of radiation informs the sensitivity of each qubit to cosmic rays that penetrate the device substrate. Our findings reveal qubit device architectures that are less susceptible to the quasiparticles created by radiation absorption. The results of this cosmic ray coincidence measurement informs strategies that reduce the impact of ionizing radiation on quantum error correction schemes.