Stochastic resonance in a periodic superconducting array

Magnetic fluxon dynamics was studied in superconducting Nb films patterned with a periodic array of holes. A sum of weak harmonic and Gaussian white noise magnetic fields is applied to the sample at $T\ll T_{c}$ and the local magnetic response is measured with a scanning Hall sensor. We find that the fluxon jump rate in the array exhibits locking with the half-period of the harmonic magnetic drive at a certain \textquotedblleft optimal\textquotedblright\ non-zero amplitude of the white noise. Peaks in the resident time distribution and formation of the quasi-periodic flux patterns is observed. We explain our observations with the phenomenon of array enhanced stochastic resonance earlier seen in various driven non-linear systems with dynamic threshold. Implications of our results for the fluxon-based superconducting devices will be discussed.