Einstein-Böhr “gedanken” Experiment Made Real at Last

Article: published in Nature Photonics News and Views by Fernando Martín, IFIMAC researcher.

Young’s double-slit experiment with massive particles is nowadays viewed as the simplest demonstration of wave-particle duality. The question of whether it is possible to determine through which slit the particle passes while preserving the interference patterns has been the object of passionate scientific and philosophical discussions. According to Bohr’s complementarity principle, the determination of which slit the particle passes through inevitably destroys the wave aspects and implies the disappearance of the interference. Einstein disagreed with this point of view and argued that it would be possible to obtain detailed information on position and momentum by using the universally accepted laws of conservation of energy and momentum. To prove it, he suggested a “gedanken” experiment, the so called «Einstein-Böhr recoiling double-slit gedanken experiment», in which one of the two slits in Young’s experiment is allowed to move. Measuring the momentum transfer between the particle and the moving slit would allow one to identify which slit the particle passed through on its way to the screen. And this without destroying the interference pattern. In this work, Fernando Martín describes the first experimental realization of the Einstein-Böhr “gedanken” experiment by using a molecular double slit. [Full article]