PITTSBURGH--Pitt physicist Wensheng Vincent Liu has received a five-year $1.42 million grant from the Air Force Office of Scientific Research to predict and understand topological phases of quantum atomic matter (i.e., a cold ensemble of interacting atoms) under novel conditions, well beyond the standard regimes. Liu is a professor in the Department of Physics and Astronomy within the Kenneth P. Dietrich School of Arts and Sciences.
While the research is theoretical in nature, the findings are expected to motivate and guide ongoing and future experiments in atomic, molecular, and optical physics, as well as provide the models for engineering novel electronic materials of the desired quantum properties in condensed matter physics. The acquired new knowledge has the potential to find applications in the future generation of precision quantum-based devices and possibly topological quantum computers and communication technology.
Trapping ultracold atoms in optical lattices has come a long way, Liu says. A popular trend has been to use atoms to emulate condensed matter physics of electrons in solid-state materials. "But this project will venture into some unconventional directions that will enable us to study exciting, unique aspects of no prior analogue in solids, hence beyond the standard quantum regime," he says. "A whole new world of exotic states is expected to appear."
Research has flourished at the interdisciplinary frontier of the fields of condensed matter physics and atomic-molecular-optical (AMO) physics. This interface area is now widely known as cold atom physics. Physicists have developed advanced experimental techniques to trap atoms and cool them down to below a few hundred degrees of nano-Kelvin. This represents the coldest temperature regime that scientists have ever achieved. Each of these alkali-metal atoms are typically several thousand times more massive than an electron. Unlike electrons, the massive atoms do not exhibit appreciable quantum effects at room temperature, not even at the liquid nitrogen temperature. They behave fully quantum once cooled down to ultralow temperature.
The world of quantum particles behaves entirely different than the classical world. One simple consequence is that each atom at such a low temperature acts as both a wave and particle at the same time, Liu says. For the wave part, they can form interference and organize together like atom laser. "Atom laser" is a coherent matter wave, one of the most remarkable effects achieved and demonstrated in the recent years in the lab of this field.
Atoms also interact with light, and physicists have found ways to use laser beams to form light crystals to trap and manipulate the atoms. These are now widely called "optical lattices." When trapping thousands and millions of such atoms in optical lattices in the lab, one creates an interacting quantum atomic matter. A number of other interesting many-body quantum phenomena are discovered or predicted. The optical lattices turn out to be one of the most flexible physical systems. It shows unprecedented tunability through manipulating the configurations of laser beams. The research so far appears to have just scratched the surface of a field of seemingly infinite potential and possibilities.
"A whole new world of many more fascinating many-body quantum phases are waiting to be discovered," Liu says.