Experiments with levitated nanoparticles reveal role of friction at the nanoscale

Hendrik Kramers at the 1927 Solvay Conference (middle row 4th from the right)

Nanoparticles levitated in a bistable optical potential well, formed by using two infrared laser beams, have been used to directly corroborate a 77-year-old theory describing the rate of transition between the two potential wells due to ‘thermally-activated escape’ in high and low damping (friction) regimes.

Strong damping leads to increased collision rate between the particle and gas molecules, reducing net translational diffusion and hence lowering ‘escape rate’, while weak damping leads to decoupling between the particle and its environment, reducing the probability of the particle gaining enough energy to overcome the barrier.

The Kramers turnover, a phenomenon predicting a maximum in escape rate for intermediate damping, was resolved by measuring the particle position with a third laser-detector system for a range of pressures, and hence different damping, or coupling strength, between the particle and gas. The system could be useful in experimentally assessing or simulating a range of stochastic processes, in particular those dependent on pressure, and could be applied in a wide range of research fields such as protein folding, chemical reaction kinetics, stability of mechanical systems and diffusion in solids or on solid surfaces.

See phys.org for the full summary.