Harvard University researchers have finally observed the repulsive Casimir force, a quantum phenomenon that was predicted back in the 1940’s. The force comes into effect only when two particles locate themselves very close to each other, provided a few other parameters are true (see Wikipedia entry: Casimir effect). Now with new knowledge of how to use the force (no pun intended), scientists should be able to build more complicated nano devices.
“Repulsive Casimir forces are of great interest since they can be used in new ultra-sensitive force and torque sensors to levitate an object immersed in a fluid at nanometric distances above a surface,” said Federico Capasso, Robert L. Wallace Professor of Applied Physics at Harvard’s School of Engineering and Applied Sciences (SEAS), who led the study. “Further, these objects are free to rotate or translate relative to each other with minimal static friction because their surfaces never come into direct contact.”
The results from Capasso’s and his colleagues’ work will be published in tomorrow’s edition of the journal Nature. Capasso’s co-authors are Jeremy Munday, formerly a graduate student in Harvard’s Department of Physics and presently a postdoctoral researcher at the California Institute of Technology, and V. Adrian Parsegian, senior investigator at the NIH in Bethesda, Md.
The discovery builds on previous work related to the Casimir force, which was theorized by Hendrick Casimir in 1948 as both attractive and repulsive, pulling materials together under some circumstances and pushing them apart under others.
Until now, however, researchers have only been able to measure the attractive Casimir force, which, in some cases, has created headaches for nano-engineers because it can cause the components of tiny devices to stick together. Discovery of the repulsive version of the Casimir force can potentially help researchers overcome this problem.
“When two surfaces of the same material, such as gold, are separated by vacuum, air, or a fluid, the resulting force is always attractive,” explained Capasso.
Instead of using gold-coated materials, Capasso and colleagues swapped out one of the gold surfaces for one made of silica, then immersed them both in a liquid, bromobenzene. That combination did the trick, switching the attractive Casimir force to repulsive. The Harvard researchers have filed for a U.S. patent covering nanodevices based on quantum levitation.
Harvard news office press release: Researchers see exotic force for first time…
NIH press release: Researchers Levitate Object at a Microscopic Scale …
Image: An artist’s rendering shows a gold sphere, in the foreground, immersed in bromobenzene, allowing it to levitate above a silica plate. When the plate is replaced by one of gold, as seen in the background, levitation is impossible. Image courtesy of Federico Capasso/SEAS