Entangled Atoms make Symmetrical Molecules look Non-Symmetrical

Molecules such as nitrogen and oxygen are made up of two identical atoms. The molecules are symmetrical in the sense that one atom cannot be distinguished from another. One could imagine that this symmetry is broken if one removes one electron from one of the atoms in the molecule. However, one can never tell whether it is the atom on the left or the right that is missing the electron. The symmetry is preserved in a state that is a combination of the electron missing from the left or the right atom.

This is one of the strange consequences of quantum mechanics that seems to defy common sense. The famous thought experiment with Schrödinger's cat was designed to show how absurd the principle is - where a cat in a closed box can be in a state where it is neither alive nor dead, but a combination of both states, until you open the box and look.

Already twenty years ago it was known that certain rules apply to the scattering of X-ray light, which depend on the molecular symmetry. In previous experiments, where an electron is removed by irradiating molecules with X-ray light, it looked like the scattering of the light takes place in one and the same place and not on the individual atoms. The reason for this is that the atoms are simply very close together. But what has not been considered is that it actually takes some time for the X-ray light to travel from the left to the right atom. This means that it is possible to remove an electron from the different atoms at different times. The time it takes for the light to travel from one atom to the other is much less than an attosecond (10-18 s), and the consequences of this short temporal delay is seen in the scattering pattern. This shows that the X-ray light is scattered on two entangled oxygen atoms.

In the new research study, Uppsala researchers together with researchers at the MAX IV laboratory in Lund have built a unique measuring station with a ten-meter long X-ray spectrometer that can rotate around the sample. They have used this instrument to measure this scattering pattern from an oxygen molecule.

The scattering pattern shows a similar interference pattern that occurs in the double-slit experiment that Thomas Young constructed to show the wave nature of light in the 19th century. In the new study, the researchers have shown that a similar interference pattern occurs due to the fact that the atoms are entangled.

– Now we connect the well-known double-slit experiment with modern quantum mechanics. Thus, we can see that when an electron is removed from one of the oxygen atoms, the two atoms become entangled, says Johan Söderström, senior lecturer at the Department of Physics and Astronomy and research leader for the project.

The new findings implies that several previous experimental results in the field have to be reinterpreted. The fact that the effects of the entanglement have now been understood, implies that the method can also be used to investigate weakly bound oxygen molecules. This applies in many vital processes, for example in the transport of oxygen molecules from the lungs to the blood or in modern technology. Notably, it also has direct implications for the role of oxygen molecules bound in battery cathodes.

Article reference

Johan Söderström et al., Parity violation in resonant inelastic soft x-ray scattering at entangled core holes. Sci. Adv.10, eadk3114 (2024). DOI:10.1126/sciadv.adk3114