  Microwave resonators with high quality factors have enabled many recent
breakthroughs with superconducting qubits and photon detectors, typically
operated in shielded environments to reduce the ambient magnetic field.
Insufficient shielding or pulsed control fields can introduce vortices, leading
to reduced quality factors, although increased pinning can mitigate this
effect. A narrow slot etched into the resonator surface provides a
straightforward method for pinning enhancement without otherwise affecting the
resonator. Resonators patterned with such a slot exhibited over an order of
magnitude reduction in the excess loss due to vortices compared with identical
resonators from the same film with no slot.
