Can antimatter bend light

Scientists offer "large designer atoms" upon request

In the not too distant future, researchers may be able to build atoms according to their specifications with one click. It's still science fiction, but a team at the University of Colorado Boulder reports it's getting closer and closer when it comes to controlling and assembling particles called "big atoms."

The new research that is in Nature published, focuses on colloidal particles which, when mixed with liquid crystals, act similar to the elements of the periodic table. These particles give physicists the ability to study how hydrogen, helium, and other atoms behave and interact without having to zoom down to the atomic level.

For example, by exposing the large atoms to different types of light, the team showed that it could turn its charge with a flick of the wrist. In other words, particles that once attracted each other are now repelling each other.

"Because we have so much control, we have the ability to design how these particles are composed and what properties they have," said Ivan Smalyukh, professor in the Department of Physics. "It's like a designer toolkit."

This designer toolkit starts with one simple component: liquid crystals.

These materials, which ensure the sharp images on the screen of your smartphone, often consist of molecules in a tidy arrangement, such as rods that all point in one direction.

However, over the past decade, scientists have noticed something strange about these liquid-like materials. When particles, like microscopic silica, are dropped into liquid crystals, the once ordered molecules inside will bend and compress to make room for the new additions.

And what is remarkable is that the way these liquid crystals bend can be mathematically analogous to the structures of the electron shells of atoms.

"How the liquid crystals bend around the particles is very important," says Smalyukh, also in the Materials Science Engineering Program and Department of Electrical, Computer, and Energy Engineering. "If you disturb these molecules, it costs energy, and this energy drives interesting interactions."

If you bend the liquid crystal molecules just right, the pieces of silicon dioxide clump into one another as if they were two atoms joining together - only much larger.

The problem, Smalyukh said, is that until recently, scientists had very little control over the interactions of these "big atoms". His group had the solution.

To make their unique colloidal mixture, Smalyukh and his colleagues used silicon dioxide pieces in the shape of hexagons for their large atoms. But before dipping these particles into liquid crystals, the researchers coated them with a type of dye that changes when exposed to different types of light.

If the researchers exposed their mixture to a certain type of blue light, the liquid crystal molecules would bend around the hexagons in a pattern. If you use a different kind of light and they would bend in a completely different way.

The group reported that they could switch the effective charge of a large atom from positive to negative and back again as they pleased.

"It's almost like using light to turn matter into antimatter," said Ye Yuan, a postdoc in physics and lead author of the new study. Other co-authors were the postdocs Qingkun Liu and Bohdan Senyuk.

And, said Yuan, the team was able to control these interactions with an ordinary lamp with a filter on it - no high power lasers required.

"Basically, we could have a good, sunny day in Colorado and take our samples outside and see these interactions," said Yuan.

What excites him, what the team was able to build with these large atoms. The researchers believe that with the right settings, they could use their method to assemble particles in unique ways and create faux-atomic structures that don't exist in nature - then they dissolve those structures just as easily.

"In a way, we still have to figure out what to do with it," said Smalyukh.