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BP: Fachverband Biologische Physik

BP 27: Nonequilibrium Processes and Self-Organisation

BP 27.4: Talk

Friday, March 30, 2007, 11:30–11:45, H43

The Einstein relation generalized to non-equilibrium — •Valentin Blickle¹, Thomas Speck², Christoph Lutz¹, Udo Seifert², and Clemens Bechinger¹ — ¹2. Physikalisches Institut, Universität Stuttgart — ²II. Institut für Theoretische Physik, Universität Stuttgart

Thermodynamics and classical statistical mechanics are not able to describe processes far from equilibrium. Recently, several exact theoretical relations, e.g. Jarzynski equation [1] and other fluctuation theorems were derived for this regime. We focuss on the Einstein relation, a prominent example of the fluctuation dissipation theorem, connecting the diffusion constant and the mobility which is violated beyond linear response. In our experiment we test its recent theoretical generalization [2] to the non-equilibrium regime. With video microscopy we observe the motion of a driven Brownian colloidal particle trapped within a torroidal 3d laser trap. Additionally we can modulate the laser intensity, imposing a stationary potential onto the torus. Using the measured particle trajectory we determine an integral over velocity correlation functions which quantifies the violation of the Einstein relation. The fact that this integral cannot be neglected demonstrates that in our experiment we are probing a regime which is far from thermal equilibrium and beyond linear response.

[1] C. Jarzynski, Phys. Rev. Lett. 78, 2690 (1997).

[2]T. Speck, U. Seifert, Europhys. Lett. 74, 391 (2006).