(ORDO NEWS) — Physicists have just caught light acting as the “glue” between atoms in a kind of loosely bound molecule.
“For the first time, we have succeeded in polarizing several atoms together in a controlled manner. , creating a measurable force of attraction between them,” says Matthias Sonnleitner, a physicist at the University of Innsbruck.
Atoms join together to form molecules in a variety of ways, all of which involve charge exchange as a kind of “superglue”.
Some share their negatively charged electrons, forming relatively strong bonds, like the simplest two oxygen atoms we breathe together with complex hydrocarbons floating in space. Some atoms are attracted due to differences in their overall charge.
Electromagnetic fields can change the arrangement of charges around an atom. Since light is a rapidly changing electromagnetic field, a shower of well-directed photons can push electrons into positions that – theoretically – could lead to their bonding.
“If you turn on an external electric field now, this charge distribution shifts a bit,” explains physicist Philipp Haslinger of the Technical University of Vienna (TU Wien).
“The positive charge shifts a little in one direction, the negative one in the other, the atom suddenly has a positive and a negative side, it becomes polarized.”
Haslinger, TU Vienna atomic physicist Mira Maiwoger and her colleagues used ultracold rubidium atoms to demonstrate that light can indeed polarize atoms in much the same way that it in turn makes neutral atoms a little sticky.
“It’s a very weak attractive force, so you have to experiment very carefully to be able to measure it,” Meiweger says.
“If the atoms have a lot of energy and move fast, the force of attraction immediately disappears. That’s why the cloud of ultracold atoms was used.”
The team captured a cloud of about 5,000 atoms under a gold-plated chip in a single plane using a magnetic field.
This is where they cooled the atoms to temperatures approaching absolute zero (-273°C or -460°F), forming a quasi-condensate – so that the rubidium particles begin to act collectively and share properties, as if they were in the fifth state of matter, but not quite. to the same extent.
Struck by the laser, the atoms experienced various forces. For example, the radiation pressure of incident photons can push them along the light beam. Meanwhile, the responses of the electrons can pull the atom back to the most intense part of the beam.
To detect the subtle attraction thought to develop between atoms in this flow of electromagnetism, the researchers needed to take some careful steps. calculations.
When they turned off the magnetic field, the atoms fell freely for about 44 milliseconds before reaching the laser light field, where they were also imaged using light fluorescence microscopy.
During the fall, the cloud naturally expanded, so the researchers were able to take measurements at different densities.
At high density, Meiweger and his colleagues found that up to 18% of the atoms were missing. observational images they made. They believe this absence was caused by light-assisted collisions ejecting the rubidium atoms from their cloud.
This demonstrated part of what was happening – it was not just incident light. acting on atoms, but also scattering light on other atoms. When light touched atoms, it gave them polarity.
Depending on the type of light used, the atoms were either attracted or repelled by the greater light intensity. Thus, they were either pulled into an area of lower or stronger light – in each case they ended up piling up together.
“The essential difference between conventional radiative forces and [evoked light] is that the latter is an effective interaction between particles mediated by scattered light,” Maiwoger and colleagues write in their paper.
“It doesn’t capture atoms in a fixed position (like the focus of a laser beam), but it pulls them towards regions with the highest particle density.”
Although this atom-picking force is much weaker than the molecular forces we are more familiar with, on a large scale it can add up. This can change the emission patterns and resonance lines, features that astronomers use to inform us about celestial objects.
It could also help explain how molecules form in space.
“In the vastness of space, small forces can play a significant role,” says Haslinger.
“Here, for the first time, we were able to show that electromagnetic radiation can create a force between atoms, which could help shed new light on astrophysical scenarios that have not yet been explained.”
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