Researchers at the University
of Pittsburgh have made
advances in better understanding correlated quantum matter that could change
technology as we know it, according to a study published in Nature.
W. Vincent Liu, associate professor of physics in Pitt’s Department
of Physics and Astronomy, in collaboration with researchers from the University of Maryland
and the University of Hamburg in England, has been studying
topological states in order to advance quantum computing. Through his research,
with more than $1 million in funding from two consecutive four-year grants from
the U.S. Army Research Office and a five-year shared grant from the DARPA
Optical Lattice Emulator Program, Liu and his team have been studying orbital
degrees of freedom and nano-Kelvin cold atoms in optical lattices (a set of
standing wave lasers) to better understand new quantum states of matter.
From that research, a surprising topological semimetal has emerged.
“We never expected a result like this based on previous studies,” says Liu. “We were surprised to find that such a simple system could reveal itself as a
new type of topological state—an insulator that shares the same properties as a
quantum Hall state in solid materials.”
Since the discovery of the quantum Hall effect by Klaus Van Klitzing in
1985, researchers like Liu have been particularly interested in studying
topological states of matter, that is, properties of space unchanged under
continuous deformations or distortions such as bending and stretching. The
quantum Hall effect proved that when a magnetic field is applied perpendicular
to the direction a current is flowing through a metal, a voltage is developed
in the third perpendicular direction. Liu’s work has yielded similar yet
remarkably different results.
“This new quantum state is very reminiscent of quantum Hall edge states,”
says Liu. “It shares the same surface appearance, but the mechanism is entirely
different: This Hall-like state is driven by interaction, not by an applied
Liu and his collaborators have come up with a specific experimental design
of optical lattices and tested the topological semimetal state by loading very
cold atoms onto this “checkerboard” lattice. Generally, these tests result in
two or more domains with opposite orbital currents; therefore the angular
momentum remains at zero. However, in Liu’s study, the atoms formed global
rotations, which broke time-reversal symmetry: The momentum was higher, and the
currents were not opposite.
“By studying these orbital degrees of freedom, we were able to discover
liquid matter that had no origins within solid-state electronic materials,”
Liu says this liquid matter could potentially lead toward topological
quantum computers and new quantum devices for topological quantum
telecommunication. Next, he and his team plan to measure quantities for a
cold-atom system to check these predicted quantum-like properties.