Quantum Wave Filmed For The First Time In Helium Dimer

Quantum physics is one field which is full of surprises. We get to know a new thing every day. 

Reinhard Dörner and his team are working with molecules which actually are not existent according to a few books: Helium compounds with two atoms. Helium Dimers are compounds of helium with two atoms. We know helium is a noble gas as it does not form any compounds. 

These helium dimers form rarely when the gas is cooled to just 10 degrees above absolute zero (minus 273 °C) and then pumped through a small nozzle into a vacuum chamber (this makes it even colder). These molecules are the weakest bound stable in the Universe, the two atoms in the molecule are extremely far apart from each other. A chemical compound containing two atoms usually measures about 1 angstrom (0.1 nanometers) whereas helium dimers measure 50 times as much (52 angstroms) on an average.    

The scientists irradiated such helium dimers with an extremely powerful laser flash, which slightly twisted the bond between the two helium atoms, which was enough to make the two atoms fly apart. This was the first time they saw a helium atom flying away as a wave and they recorded it on film. 

Quantum physics says objects have particle and wave nature at the same time. We are familiar with light particles (photons) which show this particle and wave nature. 

Researchers could observe and film the helium atom flying away as a wave at all in their laser experiment because the helium atom only flew away with a certain probability: With 98 % probability it was still bound to its second helium partner, with 2 % probability it flew away.    

Measurement of such quantum waves can be extended to quantum systems with several partners like helium trimer composed of three helium atoms. Helium trimer is of interest as it can form what is referred to as an “exotic Efimov state,” says Maksim Kunitski, first author of the study: “Such three-particle systems were predicted by Russian theorist Vitaly Efimov in 1970 and first corroborated on caesium atoms”.

 The Efimov state was discovered in the helium trimer five years ago. This laser pulse irradiation method we’ve developed might allow us to observe the formation and decay of Efimov systems and thus better understand quantum physical systems that are difficult to access experimentally.

Journal Reference:
Maksim Kunitski, Qingze Guan, Holger Maschkiwitz, Jörg Hahnenbruch, Sebastian Eckart, Stefan Zeller, Anton Kalinin, Markus Schöffler, Lothar Ph. H. Schmidt, Till Jahnke, Dörte Blume, Reinhard Dörner. Ultrafast manipulation of the weakly bound helium dimer. Nature Physics, 2020; DOI: 10.1038/s41567-020-01081-3

Press Release: Goethe University Frankfurt