Stable Casimir equilibria and quantum trapping

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Science  07 Jun 2019:
Vol. 364, Issue 6444, pp. 984-987
DOI: 10.1126/science.aax0916

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Something repulsive in the Casimir effect

Two uncharged objects (metal plates for instance) will experience an attractive force between them, the magnitude of which increases as they are brought closer together. This force, or Casimir effect, is caused by vacuum fluctuations of the electromagnetic field. Effectively, more modes outside than between the objects results in the objects being pushed together. Zhao et al. show that the extent of the electromagnetic fluctuations can be controlled by coating one of the objects with a dielectric (Teflon), which changes the Casimir effect to a repulsive force at small distances. This then cancels out the force between plates and produces a point of stable equilibrium.

Science, this issue p. 984


The Casimir interaction between two parallel metal plates in close proximity is usually thought of as an attractive interaction. By coating one object with a low–refractive index thin film, we show that the Casimir interaction between two objects of the same material can be reversed at short distances and preserved at long distances so that two objects can remain without contact at a specific distance. With such a stable Casimir equilibrium, we experimentally demonstrate passive Casimir trapping of an object in the vicinity of another at the nanometer scale, without requiring any external energy input. This stable Casimir equilibrium and quantum trapping can be used as a platform for a variety of applications such as contact-free nanomachines, ultrasensitive force sensors, and nanoscale manipulations.

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