  Superconducting circuits have attracted growing interest in recent years as a
promising candidate for fault-tolerant quantum information processing.
Extensive efforts have always been taken to completely shield these circuits
from external magnetic field to protect the integrity of superconductivity.
Surprisingly, here we show vortices can improve the performance of
superconducting qubits by reducing the lifetimes of detrimental
single-electron-like excitations known as quasiparticles. Using a contactless
injection technique with unprecedented dynamic range, we quantitatively
distinguish between recombination and trapping mechanisms in controlling the
dynamics of residual quasiparticles, and show quantized changes in
quasiparticle trapping rate due to individual vortices. These results highlight
the prominent role of quasiparticle trapping in future development of
superconducting qubits, and provide a powerful characterization tool along the
way.
