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. ; Comment: 8 pages with 4 figures for the main text, 13 pages with 11 figures for supplementary material