Figure 2

(a) Power spectrum map versus perpendicular field measured on Sample #1, in a case when vortices have opposite core polarities. The injected current through the two pillars is I_dc = 50 mA. Insert shows evolution of frequencies versus field for the non-synchronized oscillators and their predicted linear evolution. Power spectra obtained at (b) 0.5 kOe and (c) 0.7 kOe, before (b) and after (c) synchronization is achieved.