Historical research guide · 0847 · 2011
The Casimir effect in microstructured geometries
Alejandro W. Rodriguez · Federico Capasso · Steven G. Johnson
In one minute
Alejandro Rodriguez, Federico Capasso and Steven Johnson wrote the invited review that turned the Casimir force from a curiosity into an engineering variable. Hendrik Casimir predicted in 1948 that two metal plates in vacuum would attract, because the quantum fluctuations of the electromagnetic field between them are not the same as the fluctuations outside them. The authors point out that at submicrometre spacings this force is large enough to matter in real micromechanical devices, where it pulls moving parts into contact. Their central argument is that the force is not a fixed law of distance: through its close connection to classical photonics it depends strongly on the shapes and the materials of the objects, and decades of work have gone into finding geometries where it behaves nothing like Casimir’s simple attraction. They survey what that search has produced — predicted repulsion between vacuum-separated metals, stable suspension of one object above another, non-additive and temperature effects, and measured repulsion in fluids and unusual forces over nanotrench surfaces.
Connection
Chapter 2 needs the vacuum to be a real medium you can measure, and the Casimir force is where the laboratory touches it; chapter 6 needs that force to be shapeable, because every proposed vacuum energy device — Moddel’s asymmetric resonator, White’s Casimir cell, Chase’s tunnelling diode — depends on breaking the symmetry of the vacuum with geometry and materials. This is the review that maps how far that shaping has already been taken.
From the source
In 1948 Hendrik Casimir predicted that a generalized version of van der Waals forces would arise between two metal plates because of quantum fluctuations of the electromagnetic field. The force is a laboratory fact of the electromagnetic vacuum, not a model of it.Abstract, sentence 1; Nature Photonics 5, 211 (2011)
These forces become significant in micromechanical systems at submicrometre scales, for example in the adhesion between movable parts. At device dimensions the vacuum is an engineering load, not a theoretical correction.Abstract, sentence 2
Through its close connection to classical photonics, the Casimir force can depend strongly on the shapes and compositions of the objects involved. That dependence is what has driven a decades-long search for geometries in which the force behaves very differently from the monotonic attraction Casimir first predicted.Abstract, sentence 3
Recent theoretical developments reviewed here include predictions of Casimir repulsion between vacuum-separated metals, the stable suspension of objects, and unusual non-additive and temperature effects — that is, configurations where the total force is not the sum of the pairwise attractions and where the sign itself can be designed.Abstract, final sentence, theoretical developments
Experimental developments reviewed here include observations of repulsion in fluids, non-additive forces at nanotrench surfaces, and the influence of new material choices. The shaping of the force is measured, not only calculated.Abstract, final sentence, experimental observations
What to watch: the review frames geometry and material as the two design variables of the Casimir force, which sets the next measurement for anyone building a vacuum-energy device — a stable, vacuum-separated equilibrium held by shape alone, without an intervening fluid, at a separation and with materials a fabricated device can actually hold.Abstract, read as the review’s programme; Nature Photonics 5, 211 to 221 (2011)
The way in
https://doi.org/10.1038/nphoton.2011.39How to cite it
Alejandro W. Rodriguez, Federico Capasso, Steven G. Johnson (2011) The Casimir effect in microstructured geometries doi:10.1038/nphoton.2011.39