  Frequency instability of superconducting resonators and qubits leads to
dephasing and time-varying energy-loss and hinders quantum-processor tune-up.
Its main source is dielectric noise originating in surface oxides. Thorough
noise studies are needed in order to develop a comprehensive understanding and
mitigation strategy of these fluctuations. Here we use a frequency-locked loop
to track the resonant-frequency jitter of three different resonator types---one
niobium-nitride superinductor, one aluminium coplanar waveguide, and one
aluminium cavity---and we observe strikingly similar random-telegraph-signal
fluctuations. At low microwave drive power, the resonators exhibit multiple,
unstable frequency positions, which for increasing power coalesce into one
frequency due to motional narrowing caused by sympathetic driving of individual
two-level-system defects by the resonator. In all three devices we probe a
dominant fluctuator, finding that its amplitude saturates with increasing drive
power, but its characteristic switching rate follows the power-law dependence
of quasiclassical Landau-Zener transitions.
