Opportunities and challenges involving repulsive Casimir forces in nanotechnology

The Casimir force, which arises from quantum electrodynamic fluctuations, manifests as an attraction between metallic surfaces spaced mere hundreds of nanometers apart. As contemporary device architectures scale down to the nano- and microscales, quantum phenomena exert increasing influence on their behaviors. Nano- and microelectromechanical systems frequently encounter issues such as components adhering or collapsing due to the typically attractive Casimir interactions. Consequently, significant efforts have been devoted to manipulating Casimir forces, aiming to transition them from attractive to repulsive. This ability holds promise for mitigating component collapse in nanodevices and facilitating the realization of quantum levitation and ultralow friction devices. Four primary strategies have been proposed for engineering repulsive Casimir forces: employing liquid media, magnetic materials, thermodynamic nonequilibrium conditions, and specialized geometries. In this review, we examine these approaches for engineering repulsive Casimir forces, analyzing their experimental feasibility, and discussing potential implementations.