Frictional lubricity enhanced by quantum mechanics

Abstract

The quantum motion of nuclei, generally ignored in the physics of sliding friction, can affect in an important manner the frictional dissipation of a light particle forced to slide in an optical lattice. The density matrix-calculated evolution of the quantum version of the basic Prandtl-Tomlinson model, describing the dragging by an external force of a point particle in a periodic potential, shows that purely classical friction predictions can be very wrong. The strongest quantum effect occurs not for weak but for strong periodic potentials, where barriers are high but energy levels in each well are discrete, and resonant Rabi or Landau-Zener tunneling to states in the nearest well can preempt classical stick-slip with nonnegligible efficiency, depending on the forcing speed. The resulting permeation of otherwise unsurmountable barriers is predicted to cause quantum lubricity, a phenomenon which we expect should be observable in the recently implemented sliding cold ion experiments.

Structural lubricity in soft and hard matter systems

“…Employing state-of-the-art experimental setups 51 , 52 , recently artificial frictional emulators consisting of finite 1D laser-cooled Coulomb ion crystals, have demonstrated Aubry-type signatures when set into motion across a periodic optical lattice under the action of an external electric field. By changing the structural mismatch between the ion chain and substrate, highly dissipative stick slip is tuned to a nearly frictionless dynamical state already at the level of just a few interacting particles 50 , revealing intriguing potential implications even into the quantum many-body regime 116 . Similarly, by effectively changing the mutual interaction strength within a setup of two deformable ion chains, the spatially resolved position of the trapped particles has revealed an Aubry structural phase transition between a free-sliding arrangement of the chain and a pinned fractal-like atomic configuration 52 .…”

Kinks and nanofriction: Structural phases in few-atom chains

“…This work could enable the study of interacting topological defects and frustration at a nanocontact [12]. Furthermore, quantum tunnelling of ions through lattice barriers, in principle realizable in our system [40][41][42], could introduce a quantum-mechanical picture of kinks with relevance at the nanoscale and at cold surfaces.…”

Recent highlights in nanoscale and mesoscale friction

“…Inspired by earlier theoretical suggestions [ 151 – 154 ], a laser-cooled Coulomb crystal of ions, set into motion across a periodic optical lattice under the action of an external electric field, demonstrates the feasibility to control friction. By changing the structural mismatch between ion and substrate, as predicted by many-particle models, highly dissipative stick–slip can be tuned to a nearly frictionless dynamical state already at the level of just a few interacting atoms [ 148 ], revealing intriguing potential implications even into the quantum many-body regime [ 155 ].…”