We present the first experimental observation of superpersistent chaotic transients. In particular, we investigate the effect of noise on phase synchronization in coupled chaotic electronic circuits and obtain the scaling relation that is characteristic of those extremely long chaotic transients.

It has been known that noise can enhance the temporal regularity of dynamical systems that exhibit a bursting behavior--the phenomenon of coherence resonance. But can the phenomenon be expected for nonbursting chaotic systems? We present a theoretical argument based on the idea of time-scale matching and provide experimental evidence with a chaotic electronic circuit for coherence resonance in nonbursting chaotic systems.