The optimal performance of many devices is notoriously deteriorated by the presence of noise. In nonlinear, e.g. bistable systems, however, the presence of noise can improve the detection of weak periodic signals. This intriguing and apparently paradoxical phenomenon which is known as stochastic resonance (SR) has lead even after more than 20 years since its discovery to general and prolonged interest. While in most experimental systems the noise – one of the most important ingredients of SR – is artificially introduced by an external source only a few cases were studied where it is inherently present. Colloids – mesoscopic particles which are coupled to a thermal bath and therefore undergo Brownian motion – are a good example of a system with intrinsic noise. Because the length and time scales in colloidal systems are conveniently accessible with experiments, they provide excellent model systems for SR experiments.
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