Researching ultra-cold chemistry, at absolute zero temperatures

Researching ultra-cold chemistry, at absolute zero temperatures

9:40 AM, 3rd November 2015
Researching ultra-cold chemistry, at absolute zero temperatures
Image shows results of two and three ultra-cold fermionic atoms trapped in a double well confinement and interacting strongly (repulsion and attraction) and showing formation of entangled states and highly correlated molecules.

ATLANTA, US: Researchers at the Georgia Institute of Technology have received a $900,000 grant from the US Air Force Office of Scientific Research (AFOSR) to study the unusual chemical and physical properties of atoms and molecules at ultra-cold temperatures approaching absolute zero, the temperature at which all thermal activity stops.

Developing and employing advanced computational methodologies, they will explore the formation of novel types of molecular aggregates at these extreme conditions, where quantum mechanical principles govern and dramatically alter the ways that atoms and molecules interact.

 The work could help provide a better understanding of the reaction processes underlying strongly correlated atoms and molecular quantum systems in conditions unlike those seen in conventional chemistry.

“Bringing atoms together to make a new material is the basis of chemistry, but here we are synthesizing new materials through quantum mechanical forces,” said Uzi Landman, a Regent’s and Institute and Callaway Chair prof in the Georgia Tech School of Physics. “We expect to help lay the foundation for a new theory describing the chemistry of ultra-cold atoms. To do this, we will develop a different type of computational theory.”

Absolute zero is the temperature at which all thermal activity stops. The researchers will be studying matter at ultra-cold temperatures, which are in the micro-kelvin or nano-kelvin ranges closely approaching that level. At these extremely low temperatures, atoms and molecules move much more slowly and have different kinds of interactions. These atoms and molecules interact via their wave nature, with interference between waves either destroying or amplifying one another.

At these ultra-cold temperatures, the wave nature of matter also changes. For instance, the size of the de Broglie wavelength is inversely proportional to the square of the temperature, meaning wavelengths become larger as the temperature drops.

“The wavelength of a particle, say a lithium atom, taken from room temperature to one nano-kelvin, grows by a factor of about 600,000, from about 0.04 nanometre at room temperature to 24,000 nanometre (24 microns) at the lower temperature which is a very dramatic change,” Landman explained.

In conventional chemistry, activation barriers must be overcome before atoms can exchange electrons to bind together. Because they have so little energy at ultra-cold temperatures, atoms cannot overcome this activation barrier, meaning interactions must occur through other mechanisms including quantum tunnelling effects.

And at these conditions, quantum mechanical effects become more pronounced, with the long-distance entanglement of atoms affecting the physical and chemical states of the matter.

“These are pure and deep quantum mechanical objects, and they exist only at these low temperatures because the wave effect takes over,” noted Landman, who is also director of the Georgia Tech Center for Computational Materials Science (CCMS).

© Georgia Institute of Technology News

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