Using a laser beam, Austrian researchers managed to polarize several atoms simultaneously so that they are mutually attracted. Creating a single bond state significantly weaker than the bond between two atoms in a typical molecule.
A “molecule” of light and matter
While this unusual connection had long been predicted, scientists from the University of Innsbruck and the Technical University of Vienna were recently able to measure it for the first time in laboratory experiments. According to them, such a breakthrough might notably make it possible to manipulate atoms very cold and improve our understanding of how molecules form in space.
« In an electrically neutral atom, a positively charged atomic nucleus is surrounded by a cloud of negatively charged electrons “, explains Philipp Haslinger, lead author of the new study, published in the journal Physical Review X. « When you activate an external electric field, this distribution is noticeably changed and the atom polarized, with essentially a negative side and a positive side. »
Creating a polarization effect with laser light is possible because the latter is similar to a rapidly changing electromagnetic field. Therefore, it will polarize all atoms (when placed next to each other) in the same way: positive on the left and negative on the right, or vice versa. In both cases, two neighboring atoms have opposite charges, creating an attractive force between them.
« As this is a very weak force, a careful experimental protocol was needed to measure it. “, explains Mira Maiwöger, co-author of the study. ” Highly energetic, fast-moving atoms are likely to cause it to disappear immediately, so we used a cloud of ultracold atoms [ou condensat de Bose-Einstein]. »
Clouds of falling atoms
The approach consisted in capturing thousands of atoms using a magnetic trap (a chip coated in gold) and then cooling them to temperatures close to absolute zero (-273°C) in order to reduce their energy levels to a minimum. When its magnetic field was deactivated, the cloud of atoms fell in free fall and began to grow, but this phenomenon was slowed down by the polarization of the atoms carried out using a laser beam, allowing researchers to measure this force of attraction for the first time.
« Polarizing individual atoms with laser beams is nothing new. The crucial element of our experiment is that we succeeded for the first time in polarizing several atoms together in a controlled way, thus creating a quantifiable force of mutual attraction. explains Matthias Sonnleitner, who supervised the experiment.
« While this force is obviously an additional tool for controlling ultracold atoms, such work also has implications in the field of astrophysics. », estime Haslinger. « In the vastness of space, small forces can play an important role. Here we were able to show for the first time that electromagnetic radiation can generate a force between atoms, which might help illuminate some scenarios that have not yet been able to be explained.. »