Georgia Tech researchers use ultra cold chemistry to study atoms

The US Air Force Office of Scientific Research has awarded $900,000 to researchers at the Georgia Institute of Technology to study the unusual chemical and physical properties of atoms and molecules at micro-kelvin temperature ranges approaching absolute zero, the temperature at which all thermal activity stops. Atoms and molecules move much slower at extremely low temperatures and have different kinds of interactions. The experiment will explore the formation of novel types of molecular aggregates at these temperatures and could 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 Professor and Callaway Chair Professor 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.”

Landman’s research group has spent over three decades analyzing the interactions of matter using advanced computational techniques. He expects the ultra cold methodologies will help address problems the team has been otherwise unable to solve. “We will attempt to revolutionize the ability to compute things that aren’t computable at this point,” he said. “Experiments with ultra cold atoms emulate an analog-simulator mapping onto the requisite microscopic Hamiltonian, approaching realization of Richard Feynman’s vision of quantum simulators that ‘will do exactly the same as nature.’ In our work, we develop and implement exact benchmark computational microscopy solutions of the system Hamiltonian, uncovering the spectral evolution, wave function anatomy and entanglement properties of the interacting fermions in the entire system parameter range. In this way we may address some outstanding problem, like high temperature superconductivity, quantum magnetism, highly correlated quantum systems and chemistry at the ultra cold extreme.”

In conventional chemistry, activation barriers must be overcome before atoms can exchange electrons to bind together. Atoms have little energy at ultra cold temperatures and cannot overcome this activation barrier. Interactions, therefore, must occur through other quantum effects that are also impacted by the extreme cold. Quantum mechanical effects, for example, become more pronounced, with the long-distance entanglement of atoms affecting the physical and chemical states of matter. “These are pure and deep quantum mechanical objects, and they exist only at these low temperatures because the wave effect takes over,” said Landman. “The higher the degree of entanglement we have, the more robust the system is and the more certain we can be of the results. This is likely to be of importance for future progress in the areas of quantum information and computations.”

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 nanometers at room temperature to 24,000 nanometers (24 microns) at the lower temperature—which is a very dramatic change,” according to Landman.

In July, the Georgia Tech Center for Computational Materials Science published a paper on this topic, “Double-Well Ultra Cold Fermions Computational Microscopy: Wave-Function Anatomy of Attractive Pairing and Wigner-Molecule Entanglement and Natural Orbitals.” The paper was co-authored by graduate student Benedikt Brandt, Constantine Yannouleas and Landman.

Landman’s team will initially study the activity of small numbers of atoms and molecules before moving on to larger groups, examining synthetic solids created by the formation of optical lattices that control the location of atoms at ultra cold temperatures. Over the past two decades, scientists have learned to trap neutral atoms by lowering the temperature and building optical structures from laser beams to capture these slow-moving atoms. By constructing layers of atoms held together in this way, scientists can create synthetic solids that are unlike any materials that can be created at conventional chemical reaction temperatures. “Instead of chemical bonds,” said Landman, “what holds them together are photons of light from the laser beams.”