Researchers Measure Elusive Repulsive Force From Quantum Fluctuations

Cambridge - Harvard - Researchers from Harvard University and the National Institutes of Health (NIH) have measured, for the first time, a repulsive quantum mechanical force that could be harnessed and tailored for a wide range of new nanotechnology applications. The study, led by Federico Capasso, Robert L. Wallace Professor of Applied Physics at Harvard's School of Engineering and Applied Science (SEAS), will be published as the Jan. 8 cover story of Nature. The discovery builds on previous work related to what is called the Casimir force. While long considered only of theoretical interest, physicists discovered that this attractive force, caused by quantum fluctuations of the energy associated with Heisenberg's uncertainty principle, becomes significant when the space between two metallic surfaces, such as two mirrors facing one another, measures less than about 100 nanometers. "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. Remarkably, but in keeping with quantum theory, when the scientists replaced one of the two metallic surfaces immersed in a fluid with one made of silica, the force between them switched from attractive to repulsive.