Underground Measurement of Correlated Charge Noise in Superconducting Qubits

Particle interactions in a superconducting qubit chip can cause phonon excitation and trapped charges. The phonons can be absorbed by the superconductor and generate non-equilibrium quasiparticles that can tunnel across the Josephson junction and interact with the qubit energy. Trapped charges change the electric field environment over long timescales and cause charge noise in charge-sensitive qubits. Large energy deposits, such as those from ionizing radiation, can cause such behavior across multiple qubits on the same chip, correlated in space and time. We present results from recent measurements of an array of weakly charge-sensitive superconducting qubits exposed to a range of radiation fluxes in an underground, low-background environment. We discuss the relationship between gamma flux and qubit charge noise.