  Brownian microparticles diffusing in optical potential energy landscapes
constitute a generic testbed for nonequilibrium statistical thermodynamics and
has been used to emulate a wide variety of physical systems, ranging from
Josephson junctions to Stirling engines. Here we demonstrate that it is
possible to scale down this approach to nanometric length-scales by
constructing a tilted washboard potential for the rotation of plasmonic gold
nanorods. The potential depth and tilt can be precisely adjusted by modulating
the light polarization. This allows for a gradual transition from continuous
rotation to discrete stochastic jumps, which are found to follow Kramers
dynamics in excellent agreement with stochastic simulations. The results widen
the possibilities for fundamental experiments in statistical physics and
provide new insights in how to construct light-driven nanomachines and
multifunctional sensing elements.
