Scientists have recently observed light behaving as a sort of weakly bound molecule, acting as the “glue” connecting atoms.
According to physicist Matthias Sonnleitner of University of Innsbruck, “We’ve succeeded for the first time in polarising multiple atoms together in a controlled way, establishing a measurable attractive force between them.”
With the exchange of charges acting as a sort of “superglue,” atoms can join to create molecules in a number of ways.
Some of these molecules create rather strong connections by sharing their negatively charged electrons, ranging from the simplest gases—the two linked oxygen atoms we breathe in continuously—to the complex hydrocarbons found floating in space. Some atoms are attracted to one another due to variations in their overall charge.
Charge configurations around an atom can change in the presence of electromagnetic forces. Since light is an electromagnetic field that is always changing, a suitable photon shower can move electrons into positions where they might, in theory, bond.
This charge distribution varies a little if you now turn on an external electric field, according to physicist Philipp Haslinger of Technical University of Vienna (TU Wien).
The atom is polarised when the positive charge is slightly displaced in one direction and the negative charge is significantly shifted in the other way.
Using ultracold rubidium atoms, Haslinger, atomic physicist Mira Maiwöger, & colleagues showed that light may polarise atoms in a manner similar to that of magnetic fields, which causes otherwise neutral atoms to become slightly sticky.
It takes a very thorough experiment to be able to measure such a weak attraction force, according to Maiwöger.
“The attractive force vanishes instantly when atoms are travelling quickly and with a lot of energy. The use of an ultracold atom cloud was due to this.”
The scientists used a magnetic field to confine a cloud of about 5,000 atoms beneath a gold-coated chip to a single plane.
The atoms were impacted by a laser and experienced a variety of stresses. For instance, the pressure from incoming photons’ radiation can force them to move along the light beam. As the atom moves away from the most intense section of the beam, reactions in the electrons may cause it to return.
The researchers needed to perform some thorough calculations in order to identify the slight attraction that is expected to form between atoms in this storm of electromagnetism.
The atoms free-fell for about 44 milliseconds after the magnetic field was turned off before arriving in the laser light field, where they were even imaged using light sheet fluorescence microscopy.
The cloud dynamically expanded during the fall, allowing the researchers to collect information at various densities.
Maiwöger and colleagues discovered that at high densities, up to 18% of the atoms were missing from the observational photographs they were taking. They postulate that these absences resulted from collisions that were aided by light, which forced the rubidium atoms from their cloud.
This illustrated a portion of what was going on, showing that light scattering off other atoms as well as the light coming in was having an impact on the atoms. The atoms acquired polarity when the light made contact with them.
Higher light intensity either attracted or repelled the atoms depending on the type of light used. As a result, they were either drawn to an area of lower light or more light, and in both cases, they eventually gathered together.
In their study, Maiwöger and colleagues state that one key distinction between typical radiation forces and the light-triggered interaction is that the former involves an effective particle-particle contact, mediated by scattered light.
It attracts atoms toward areas of highest particle density rather than trapping them in a fixed location (like the laser beam’s focus).
Although the force pulling the atoms together is far smaller than the molecular force we are more familiar with, it can still accumulate on vast sizes. Resonance lines and emission patterns, which astronomers use to help us understand celestial objects, may change as a result.
Additionally, it might clarify how molecules develop in space.
Small forces can have a big impact in the immensity of space, claims Haslinger.
Here, we were able to demonstrate for the first time that electromagnetic radiation may produce a force between atoms, which may assist to clarify previously unrecognised astrophysical circumstances.
Physical Review X published the results of this study.