The behaviour of optically trapped particles is the result of the interplay between a natural well-defined noisy background and a finely-controllable deterministic force field, as shown in Fig. 20.1 for the simplest case of a particle held in a harmonic optical trap. In fact, on the one hand, as we have seen in Chapter 7, colloidal particles are constantly moving due to the presence of Brownian motion, which introduces a well-defined noisy background. On the other hand, as we have seen all though this Book, it is possible to use optical forces to introduce deterministic perturba- tions acting on the particles in a very controllable way. Therefore, optically trapped particles can be a very powerful tool to study those statistical physics phenomena whose dynamics are driven by both random and deterministic forces, ranging from biomolecules and nanodevices to financial markets and human organisations. In this Chapter, we will exemplarily discuss how optically trapped particles have been em- ployed in order to study Kramers rates, stochastic resonance, spurious drift, crystal formation and anomalous diffusion.
20.1 Colloids as a model system for statistical physics
20.2 Kramers rates
20.3 Stochastic resonance
20.4 Spurious drift in diffusion gradients
20.5 Colloidal crystals and quasicrystals
20.6 Random potentials and anomalous diffusion
20.7 Further reading