Double-Slit Experiment in a New Light

An inter­national research team led by physicists from the Uni­versity of Cologne has imple­mented a new variant of the basic double-slit experiment using resonant in­elastic X-ray scattering at the European Synchro­tron ESRF in Grenoble. This new variant offers a deeper under­standing of the electronic structure of solids. The double-slit experiment is of funda­mental impor­tance in physics. More than 200 years ago, Thomas Young diffracted light at two adjacent slits, thus generating inter­ference patterns behind this double slit. That way, he demon­strated the wave character of light. In the 20th century, scientists have shown that electrons or molecules scattered on a double slit show the same inter­ference pattern, which contra­dicts the classical expectation of particle behaviour, but can be explained in quantum-mechanical wave-particle dualism. In contrast, the researchers in Cologne inves­tigated an iridium oxide crystal by means of resonant inelas­tic X-ray scattering (RIXS).

Double-slit experiment using resonant inelastic X-ray scattering on an iridium oxide crystal: An intense beam of high-energy X-ray photons hits two adjacent iridium atoms in the crystal. This excites electrons in the atoms for a short time. The atoms emit X-ray photons which overlap behind the two iridium atoms and can be analyzed as interference images. (Source: M. Grueninger, U Cologne)

The crystal is irra­diated with strongly colli­mated, high-energy X-ray photons. The X-rays are scattered by the iridium atoms in the crystal, which take over the role of the slits in Young’s classical experi­ment. Due to the rapid technical develop­ment of RIXS and a skilful choice of crystal structure, the physicists were now able to observe the scattering on two adjacent iridium atoms, a dimer. “The inter­ference pattern tells us a lot about the scat­tering object, the dimer double slit”, says Markus Grüninger, who heads the research group at the Uni­versity of Cologne. In contrast to the classical double-slit experiment, the inelas­tically scattered X-ray photons provide infor­mation about the excited states of the dimer, in parti­cular their symmetry, and thus about the dynamic physical pro­perties of the solid.

These RIXS experi­ments require a modern synchro­tron as an extremely brilliant X-ray light source and a sophis­ticated experi­mental setup. To specifically excite only the iridium atoms, scientists have to select the very small pro­portion of photons with the right energy from the broad spectrum of the synchro­tron, and the scattered photons are selected even more strictly accor­ding to energy and direction of scattering. Only a few photons remain. With the required accuracy, these RIXS experiments are currently only possible at two synchro­trons worldwide, including the ESRF – European Synchro­tron Radia­tion Facility – in Grenoble, where the team from Cologne conducted their experiment.

“With our RIXS experiment, we were able to prove a funda­mental theo­retical prediction from 1994. This opens a new door for a whole series of further experi­ments that will allow us to gain a deeper under­standing of the properties and func­tionalities of solids”, says Grüninger. (Source: U. Cologne)

Reference: A. Revelli et al.: Resonant inelastic x-ray incarnation of Young’s double-slit experiment, Sci. Adv. 5, eaav4020 (2019); DOI: 10.1126/sciadv.aav4020

Link: Group Grüninger, II. Institute of Physics, University of Cologne, Cologne, Germany

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