Quantum Force Turns Repulsive

摘要

The experimental verification that a bizarre quantum effect - the Casimir force - can manifest itself in its repulsive form is pivotal not only for fundamental physics but also for nanotechnology. In 1948, Hendrik Casimir predicted that two uncharged, perfectly conducting plates in a vacuum would be attracted to each other because of quantum fluctuations in the vacuums electromagnetic field between the plates. Generalized for real materials by Evgeny Lifshitz in 1956, Casimir s prediction has been verified many times and is now known as the Casimir-Lifshitz (C-L) force. But for all systems studied experimentally so far, the C-L force is attractive. Writing in this issue (page 170), Munday et al. report the first experimental measurement of a repulsive C-L force. The attractive C-L force has been measured with great precision, and has been taken into account in the design of nanoscale mechanical devices. But in many instances, the attractive nature of the force has led to more problems than solutions. One such problem is that the components in a nanodevice can stick together irreversibly. The desirability of a repulsive C-L force stems from its potential to fix this problem and also to enable objects to be levitated in fluids, which could find applications in nanotechnology. Proposals for the design of 'metamaterials' capable of producing such a repulsive force have been put forward, but attempts to achieve this have been unsuccessful. Munday and colleagues' experiment is based on a further generalization of Lifshitz's formulation of the force, which allows the vacuum to be replaced by a material - here, a liquid.