Physicists Finally Measure A Long Theorized Molecule Made From Light And Matter


 Illustration of atoms made sticky by a beam of light. (Harald Ritsch/TU Wien)

Physicists have just observed light acting the part of 'Glue' between atoms, in a kind of loosely bonded molecule. 

"We have succeeded getting a good result for the first time in polarizing several atoms together in a controlled way, establishing a measurable attractive force between them," says University of Innsbruck Professor Matthias Sonnleitner. 

Atoms connect to create molecules in a number of ways, all involving a trade of charges as a kind of 'Superglue'. 

Some share their negatively charged electrons, creating relatively strong bonds, like the simplest gasses of two conjoined oxygen atoms we continuously breathe in, to the complex hydrocarbons found floating in space. Few atoms attract by virtue of differences in their overall charge. 

Electromagnetic fields can change the positionings of charges around the atom. Since light is a rapidly altering electromagnetic field, a shower of appropriately directed photons can push the electrons into positions that – in theory – could see them bond. 

"If you now switch on an external electric field, this charge distribution moves a little bit," explains senior physicist Philipp Haslinger from the Technical University of Vienna (TU Wien). 

Haslinger, TU Wien Atomic Physicist Mira Maiwöger and his team used ultracold rubidium atoms to show that light can indeed polarize atoms in much the very same way, which in turn makes otherwise neutral atoms gets a little sticky.  

"If atoms have large amount of energy and are moving rapidly, the attractive force is gone immediately. This is why a cloud of extremely cold atoms was used." 

The team trapped a cloud of around 5,000 atoms under a gold-coated chip, in a single plane, using a magnetic field. 

This is where they cooled down the atoms down to absolute zero (−273 °C or −460 °F), creating a Quasi condensate – so the particles of rubidium begin acting collectively and sharing properties like they're in the fifth state of matter, but not quite to very same extent. 

To observe the subtle attraction thought to arise between atoms in this torrent of electromagnetism, the researchers needed to do some careful measurements. 

At high densities, Maiwöger and his team found up to 18 percent of the atoms were missing from the observational pictures they were capturing. They anticipate these absences were due to light-assisted collisions kicking the rubidium atoms out from their cloud. 

"An important difference between usual radiation forces and the [light triggered] interaction is that the latter is an effectual particle-particle interaction, mediated by scattered light," Maiwöger and his team write in their paper. 

While this force assembling the atoms is a much weaker than molecular forces, we're more known with, over large scales it can add up. This can shift discharge patterns and resonance lines– features astronomers use to inform us understanding of celestial objects. 

This research was originally published in Physical Review X. 

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