Attractive and Repulsive Casimir–Lifshitz Forces, QED Torques, and Applications to Nanomachines

Abstract

This chapter discusses recent developments in quantum electrodynamical (QED) phenomena, such as the Casimir effect, and their use in nanomechanics and nanotechnology in general. Casimir–Lifshitz forces arise from quantum fluctuations of vacuum or more generally from the zero-point energy of materials and their dependence on the boundary conditions of the electromagnetic fields. Because the latter can be tailored, this raises the interesting possibility of designing QED forces for specific applications. After a concise review of the field in the introduction, high precision measurements of the Casimir force using MicroElectroMechanical Systems (MEMS) are discussed. Applications to nonlinear oscillators are presented, along with a discussion of their use as nanoscale position sensors. Experiments that have demonstrated the role of the skin-depth effect in reducing the Casimir force are then presented. The dielectric response of materials enters in a non-intuitive way in the modification of the Casimir–Lifshitz force between dielectrics through the dielectric function at imaginary frequencies ε(iξ). The latter is illustrated in a dramatic way by experiments on materials that can be switched between a reflective and a transparent state (hydrogen switchable mirrors) and by a large reduction of the Casmir force between a gold sphere and a thick gold film, when the latter is replaced by an indium tin oxide (ITO) thick film. Changing the electromagnetic density of states by altering the shape of the interacting surfaces on a scale comparable to their separation is an effective method to tailor Casimir–Lifshitz forces. Measurements of the latter between a silicon surfaces nanostructured with deep trenches and a sphere metalized with thick gold have demonstrated the non-additivity of these forces and the ability to tailor them by suitable surface patterning. Experiments on the Casimir effect in fluids are discussed, including measurements of attractive and repulsive Casimir forces conducted between solids separated by a fluid with ε(iξ) intermediate between those of the solids over a large frequency range. Such repulsive forces can be used to achieve quantum levitation in a virtually friction-less environment, a phenomenon that could be exploited in innovative applications to nanomechanics. The last part of the chapter deals with the elusive QED torque between birefringent materials and efforts to observe it. We conclude by highlighting future important directions.KeywordsDielectric FunctionCasimir ForceCasimir EnergyGold SphereCasimir EffectThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.