For the first time, an international team of
scientists from 51猎奇 and the University of Oklahoma has succeeded
in filming quantum physical effects on a helium dimer as it breaks apart. The
film shows the superposition of matter waves from two simultaneous events that
occur with different probability: The survival and the disintegration of the
helium dimer. This method might in future make it possible to track
experimentally the formation and decay of quantum Efimov systems (Nature
Physics, DOI 10.1038/s41567-020-01081-3).
FRANKFURT. Anyone
entering the world of quantum physics must prepare themself for quite a few
things unknown in the everyday world: Noble gases form compounds, atoms behave
like particles and waves at the same time and events that in the macroscopic
world exclude each other occur simultaneously.
In the world of quantum physics, Reinhard
D枚rner and his team are working with molecules which 鈥� in the sense of most
textbooks 鈥� ought not to exist: Helium compounds with two atoms, known as helium
dimers. Helium is called a noble gase precisely because it does not form any
compounds. However, if the gas is cooled down to just 10 degrees above absolute
zero (minus 273 掳C) and then pumped through a small nozzle into a vacuum
chamber, which makes it even colder, then 鈥� very rarely 鈥� such helium dimers
form. These are unrivaledly the weakest bound stable molecules in the Universe,
and the two atoms in the molecule are correspondingly extremely far apart from
each other. While a chemical compound of two atoms commonly measures about 1
angstrom (0.1 nanometres), helium dimers on average measure 50 times as much,
i.e. 52 angstrom.
The scientists in Frankfurt irradiated
such helium dimers with an extremely powerful laser flash, which slightly
twisted the bond between the two helium atoms. This was enough to make the two
atoms fly apart. They then saw 鈥� for the very first time 鈥� the helium atom
flying away as a wave and record it on film.
According to quantum physics, objects
behave like a particle and a wave at the same time, something that is best
known from light particles (photons), which on the one hand superimpose like
waves where they can pile upor extinguish each other (interference), but on the
other hand as 鈥渟olar wind鈥� can propel spacecraft via their solar sails, for
example.
That the researchers were able to observe
and film the helium atom flying away as a wave at all in their laser experiment
was due to the fact that the helium atom only flew away with a certain
probability: With 98 per cent probability it was still bound to its second
helium partner, with 2 per cent probability it flew away. These two helium atom waves 鈥� Here it comes! Quantum
physics! 鈥� superimpose and their interference could be measured.
The measurement of such 鈥渜uantum waves鈥�
can be extended to quantum systems with several partners, such as the helium
trimer composed of three helium atoms. The helium trimer is interesting because
it can form what is referred to as an 鈥渆xotic Efimov state鈥�, says Maksim
Kunitski, first author of the study: 鈥淪uch three-particle systems were
predicted by Russian theorist Vitaly Efimov in 1970 and first corroborated on
caesium atoms. Five years ago, we discovered the Efimov state in the helium
trimer. The laser pulse irradiation method we鈥檝e now developed might allow us
in future to observe the formation and decay of Efimov systems and thus better
understand quantum physical systems that are difficult to access
experimentally.鈥�
Publication:
Maksim Kunitski, Qingze Guan, Holger
Maschkiwitz, J枚rg Hahnenbruch, Sebastian Eckart, Stefan Zeller, Anton Kalinin,
Markus Sch枚ffler, Lothar Ph. H. Schmidt, Till Jahnke, D枚rte Blume, Reinhard
D枚rner: Ultrafast manipulation of the
weakly bound helium dimer. In: Nature Physics,
Pictures
to download:
Caption:
Dr Maksim Kunitski next to the COLTRIMS
reaction microscope at 51猎奇, which was used to observe the
鈥渜uantum wave鈥�. (Photo: Uwe Dettmar for 51猎奇)
Caption: Professor Reinhard D枚rner (left) and Dr Maksim Kunitzki in front of the
COLTRIMS reaction microscope at 51猎奇, which was used to observe
the quantum wave. (Photo: 51猎奇 Frankfurt)
Video:
Further information
Professor Reinhard D枚rner
Institute for Nuclear Physics
Tel.: +49 (0)69 798-47003
doerner@atom.uni-frankfurt.de
