Our spatial sense doesn't extend beyond the familiar three dimensions, but
that doesn't stop scientists from playing with whatever lies beyond.
Rice University physicists are pushing spatial boundaries in new
experiments. They've learned to control electrons in gigantic Rydberg atoms
with such precision they can create "synthetic dimensions," important tools
for quantum simulations.
The Rice team developed a technique to engineer the Rydberg states of
ultracold strontium atoms by applying resonant microwave electric fields to
couple many states together. A Rydberg state occurs when one electron in the
atom is energetically bumped up to a highly excited state, supersizing its
orbit to make the atom thousands of times larger than normal.
Ultracold Rydberg atoms are about a millionth of a degree above absolute
zero. By precisely and flexibly manipulating the electron motion, Rice
Quantum Initiative researchers coupled latticelike Rydberg levels in ways
that simulate aspects of real materials. The techniques could also help
realize systems that can't be achieved in real three-dimensional space,
creating a powerful new platform for quantum research.
Rice physicists Tom Killian, Barry Dunning and Kaden Hazzard, all members of
the initiative, detailed the research along with lead author and graduate
student Soumya Kanungo in a paper published in Nature Communications. The
study built off previous work on Rydberg atoms that Killian and Dunning
first explored in 2018.
Rydberg atoms possess many regularly spaced quantum energy levels, which can
be coupled by microwaves that allow the highly excited electron to move from
level to level. Dynamics in this "synthetic dimension" are mathematically
equivalent to a particle moving between lattice sites in a real crystal.
"In a typical high school physics experiment, one can see light emission
lines from atoms that correspond to transitions from one energy level to
another," said Hazzard, an associate professor of physics and astronomy who
established the theoretical basis for the study in several previous papers.
"One can even see this with a very primitive spectrometer: a prism!
"What is new here is that we think of each level as a location in space," he
said. "By sending in different wavelengths of light, we can couple levels.
We can make the levels look like particles that just move around between
locations in space.
"That's hard to do with light—or nanometer-wavelength electromagnetic
radiation—but we're working with millimeter wavelengths, which makes it
technically much easier to generate couplings," Hazzard said.
"We can set up the interactions, the way particles move and capture all the
important physics of a much more complicated system," said Killian, a Rice
professor of physics and astronomy and dean of the Wiess School of Natural
Sciences.
"The really exciting thing will be when we bring multiple Rydberg atoms
together to create interacting particles in this synthetic space," he said.
"With this, we'll be able to do physics that we can't simulate on a classic
computer because it gets complicated very quickly."
The researchers demonstrated their techniques by realizing a 1D lattice
known as a Su-Schrieffer-Heeger system. To make it, they used lasers to cool
strontium atoms and applied microwaves with alternating weak and strong
couplings to create the proper synthetic landscape. A second set of lasers
was used to excite atoms to the manifold of coupled, high-lying Rydberg
states.
The experiment revealed how particles move through the 1D lattice or, in
some cases, are frozen at the edges even though they have enough energy to
move, Killian said. This relates to material properties that can be
described in terms of topology.
"It is much easier to have control over coupling amplitudes when using
millimeter waves to couple Rydberg atomic states," Kanungo said. "When we
achieve that 1D lattice, with all the couplings in place, we can try to see
what dynamics would result from exciting a Rydberg electron into that
synthetic space."
"Using a quantum simulator is kind of like using a wind tunnel to isolate
the small but important effects that you care about among the more
complicated aerodynamics of a car or airplane," Killian said. "This becomes
important when the system is governed by quantum mechanics, where as soon as
you get more than a couple of particles and a few degrees of freedom, it
becomes complicated to describe what's going on.
"Quantum simulators are one of the low-hanging fruits that people think will
be early, useful tools to come out of investments in quantum information
science," he said, noting that this experiment combined techniques that are
now fairly standard in labs that study atomic physics.
"All the technologies are well-established," he said. "You could even
conceive of this becoming almost a black box experiment that people could
use, because the individual pieces are very robust."
Reference:
S. K. Kanungo et al, Realizing topological edge states with Rydberg-atom
synthetic dimensions, Nature Communications (2022).
DOI: 10.1038/s41467-022-28550-y
Tags:
Physics